Google will make the Android 5.0 SDK available today, 17th October, so head to developer.android.com/preview to check if updated Nexus 5 and 7 images are available to download. This is how owners of these devices can get the latest build of Lollipop today instead of waiting for the over-the-air update in the "coming weeks". You can follow the instructions below which explain how to install Lollipop, but make sure you're downloading the 5.0 version and not the older Android L developer preview. We expect the new SDK to be available from around 5pm UK time. Don't forget, this method is not recommended for regular users: it will ERASE your device and you will lose ALL your data.
So, you have been warned, but the good news is that you can uninstall the Android Lollipop preview and revert to factory settings. Just make sure you have backed up everything that you can't afford to lose before you install Android Lollipop, since the process will wipe your device.
We'll explain step by step how to install the preview on a Nexus 5, using Windows 7 or 8, and also how to go back to the original software that your device shipped with. The process is effectively the same on the 2013 Nexus 7.
How to install Android Lollipop
Step 1. Download the minimal 2MB installer from this XDA thread this XDA thread which includes the Android ADB and fastboot tools.
You need these to install the Android L image, and this is the quickest and easiest way to install the tools without downloading the entire Android SDK, which is huge and contains stuff you don't need to get Android L.
Follow the instructions (don't change the installation path when asked where to install it) and you should end up with a command prompt window:
Step 2. Download the appropriate file for your device:
You will also need a utility such as 7-zip which can extract the files from the .tgz archive. In fact, you'll need to unzip the files twice, as there's a .tar file inside the .tgz file. Extract the files to the same folder as the Minimal ADB and Fastboot, which is c:\Program Files (x86)\Minimal ADB and Fastboot.
Once extracted you should have a list of files as per the image below.
Step 4. Download the Google USB driver from here and extract the zip file somewhere.
Step 5. With your Nexus connected via USB and powered on, go to the Control Panel and click Devices and Printers. You should see your device in the list. On our Windows 8 machine, it was listed as ‘MTP' under Multimedia devices. Right-click on it, and choose properties. Click on the Hardware tab, then select the Nexus 5 in the list, and click Properties. Now update the driver, pointing Windows to the folder where you extracted the Google USB driver. Once done, it should report the device as Android Composite ADB interface. Plus, you should get a prompt on your device's screen asking “Allow USB debugging?”. Tick Always allow from this computer and tap OK.
Step 6. Now, Power off your device, and leave it connected to your computer's USB port. Now start it using the appropriate key combination to put it in "fastboot" mode.
For the Nexus 5, that's by holding down the volume up, volume down and power buttons simultaneously. You should see a screen like the one below. Press power and volume down on the Nexus 7.
Alternatively, you can leave your device on and type adb reboot-bootloader to restart in fastboot mode.
Step 7. If the LOCK STATE says locked (which it should) then type 'fastboot oem unlock' at the command prompt, without the quotes, and press Enter. You'll see a screen like the one below. To change from no to yes, use the volume rocker, and to select the option, press the power button.
This WILL erase your device, so make sure you've backed everything up first.
Step 8. With the bootloader unlocked, you can now install the Android L firmware. Simply type
and the process will begin. You will see alternating downloading… writing…. erasing… on your device's screen.
Step 9. When the process finished, you should lock the bootloader again for security. Start the device in fastboot mode (as in Step 6), and then type fastboot oem lock
Locking the bootloader won't wipe any data, but if you unlock it again, it will erase the device of all user data and settings.
How to uninstall Android Lollipop and return to factory settings
Reverting to the version of Android you had before installing Android L is pretty much the same process as you've just completed.
Step 10. First, download the correct version of Android KitKat for your device from Google's images page
You can choose which version of KitKat you want.
Step 11. Then, extract it as in Step 2 above. You'll need to delete the Android L files from the c:\Program Files (x86)\Minimal ADB and Fastboot folder before copying the extracted files there. These are the files to remove (in case you forgot which were which).
How to install Android L: Nexus 4 and Nexus 7 2012
Although Google has published the source code for Android L on many Nexus devices, the developer preview is only available for the Nexus 5 and 2013 edition of the Nexus 7. However, if you're super keen, you can get Android L for your Nexus 4 and the original Nexus 7 from 2012.
The developers over on XDA have managed to port Android L to both of the older devices. If you own a Nexus 4, check out this thread on getting the new Android and this thread if you have the original Nexus 7.
Be warned that these are beta versions and as such many things are not working on a basic level and apps are likely to not work. A list of issues can be found on GitHub.