Note: Please wipe all data in Recovery mode if you want to update to a discontinuous ROM version, or downgrade to an older ROM version using MIUI full ROM pack.
Download the latest MIUI ROM file Download here
There is no need to do it again if you've already downloaded the latest ROM file.
Connect your device to the Windows PC/laptop via a micro USB cable, and copy the ROM file downloaded in Step 1 into the folder 'downloaded_rom' in the internal storage of your device.
Launch 'Updater' app on your device：
MIUI 6: Click the '…' icon at the top-right corner, select 'Choose update package', and choose the ROM file you've put in 'downloaded_rom' in Step 2.
MIUI V5: Press the Menu button, select 'Choose update package', and choose the ROM file you've put in 'downloaded_rom' in Step 2.
After choosing the right ROM file, your device will begin upgrading. Your device should automatically boot to the new version when the update is completed.