download the 13977 versione from the site. upload it as a normal official release, wait 6 minutes and you're done. easy as hell.
i don't suggest you to do it, anyway. you will lost nas and torrent functionality, and it looks like it as some speed problem [you can't get over 130mbit lan].
it's pretty stable, works fine by the way...
and remember: you can't go back. a lot of people bricked their router trying to go back to the official.
the solution is wait the new official firmware or a fully working dd-wrt one.