Update From Miui 6.5.26 To 7.5.25

[Krigan_N14]

As from thread title, i would like to Update my Mi4c from the my current ROM, weekly MIUI 6.5.26 - Last Miui 7) to the more recent ROM MIUI 7.5.25 - MIUI 8.3.
Since also the Android version change, do i have to unlock the bootloader and instal it via TWRP or i can simply download the ROM here (https : //xiaomi.eu/community/threads/7-5-25.40192/) and instal it via Updater app?

Thank in advance to anybody who can help me.

 

[Krigan_N14]

Thank you very much for your advices! I'll probably do what you suggest and update to 6.12.22.