1. Unlock bootloader
2. Flash TWRP (i uploaded china twrp on this forum, use that)
3. Factory reset (do your backup before processing!) -> if you are using mi account, please remenber that's account's password or remove mi account from device
before factory reset, because you need to input mi account password to use phone after factory reset!
4. Wipe data (it will erase your internal storage. PLEASE DO YOUR BACKUP BEFORE PROCESSING!!!
5. Install rom