The upgrade method:
Method 1. Flashing full MIUI ROM pack on the phone(This part applies to all the xiaomi phone models. )
Download necessary files to prepare for flashing MIUI ROM
Flashing a newer version of MIUI ROM doesn’t need to wipe data, but flashing an older one does.
Download the multilingual MIUIROM
If you have downloaded the latest installation pack, there is no need to download it again.
Connect your phone to the computer, and put the ROM file to the folder downloaded_rom in the SD card. Open Updater on the launcher, press the Menubutton – Select installation file. Choose the ROM pack you want to flash, and select Update now.
After updating is completed, select Reboot now to enter the new system.
Method 2. Updating zip file in Recovery
Please make sure that your phone has enough power.
Download the multilingual MIUI ROM
Operate on the computer, rename the zip file as update.zip, and copy it to the root directory of the SD card. The update.zip copied from SD card to internal storage
Enter Updater, press the Menu button, and select Reboot to recovery mode.
Another way to enter recovery mode: turn off the phone, press the Volume+ key and the Power button at the same time, wait until the screen wakes.
Select yourlanguage. Select to install update.zip to system one (use the volume keys to select, and the Power button to confirm). After the updating is completed, reboot to system one.
Source: Xiaomi Device