How to install it for the first time ?:
1- Use https://github.com/acecilia/OpenWRTInvasion to gain telnet access.
3- After gaining telnet access use any ftp client to upload openwrt to /tmp/
4- Run "mtd -r write /tmp/openwrt-ramips-mt76x8-xiaomi_mi-router-4c-squashfs-sysupgrade.bin OS1" on shell to install openwrt.
5- Now wait until router reboots itself.
6- Router's IP adress is 192.168.1.1 now.
7- Go to 192.168.1.1 on your browser
8- If everything goes alright, you are on LuCI (admin panel of OpenWrt) now.
How to update from earlier versions ?
1- Go to System -> Backup/Flash Firmware.
2- Under "Flash new firmware image" browse new bin and hit upload then install.
Download from here