I also advise against installing this build. It's not so stable, the screen flickers, and you have no WiFi (couldn't enable it, tried reinstalling the build twice). Also, after a hard reset, sometimes it does not install apps like phone. Basically making it useless.
If you still want to proceed, you can find the instructions in the sticky thread about updating to 8.1.2.
Just make sure you have the flash software and a backup ROM on standby on your PC/laptop.