The procedure is explained above, but I will repeat it in details:
- download the corresponding zip file for 8.2.3 version and Mi4C (libra) on xiaomi.eu
- put it on the main storage directory of phone
- We suppose here that you have unlocked phone with TWRP installed. Disable the login pattern (I am not sure if this is necessary)
- Next go to settings/About phone/System updates and on the 3 dots up-right choose "choose update package"
- Select the zip archive you just downloaded
- It will reboot to recovery (TWRP) and install the new ROM
- You are done! All your data and apps should be working... You will not see much difference in the UI and settings!
- Now the TWRP is lost and for future updates you should unlock the bootloader again and install it.
- This is done easily: You check en.miui.com for the unlocking software. You download it on PC and follow directions there to unlock the phone. If you have done it before, it will be straight forward and done in seconds.
- Now with unlocked bootloader, install the new TWRP (3.0.3 or above) for future updates. For this, I imagine you have done in the past and you should follow the same procedure within adb environment.
You can check the new version if you go to "About phone" and hit on the software version several times