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. If you upgrade from MIUI Stable ROM based on Android M to MIUI Developer ROM based on Android N, please flash it via Fastboot update. Recovery update might cause upgrade failure.
Step 1: Download the MIUI ROM Flash file FROM HERE, There is no need to download it again if you’ve already downloaded the latest ROM file.
Step 2 : Connect your device to the Windows Computer/laptop via USB cable, and copy the Downloaded ROM file in Step 1 into the folder ‘downloaded_rom’ in the internal storage of your device SD card.
Step 3 : Launch ‘Updater’ app on your device from setting – MIUI 6/7/8
> Click the ‘…’ icon at the top-right corner, Click ‘Choose update package’ and choose the ROM file that you’ve put into ‘downloaded_rom’ in Step 2.
FOR MIUI V5 : Press the Menu button> select ‘Choose update package’, and choose the ROM file that you’ve put into ‘downloaded_rom’ in Step 2.
Step 3 : After choosing the ROM file, your device will begin upgrading automatically.The device should automatically boot to the new version when the update is completed.
💡 Remember ! when you hard reset to your smartphone, you must backup your all data, because after hard reset you lost your all important data from internal memory.We provide a link how to Backup Android Device
Credit: en.miui.com