How do I install a beta version of PlexBMC?

Probably a totally noob question but how do I install a beta version of PlexBMC?

https://forums.plex.tv/discussion/106593/plexbmc-xbmc-add-on-to-connect-to-plex-media-server/p1 - seems to include necessary basics.
Presume just finding/downloading the beta file is necessary if not the same version as that instructions.