Switching from Android Revolution HD 12 to viperonem9 questions..

I recently switched from my stock unrooted HTC One m9 to to the Android rev rom (see:http://forum.xda-developers.com/one-...0-art-t3068820) and have encountered several problems, such as freezes in gallery, phone heating a lot etc. So I've been wanting to switch to the viper one m9 3.5.0 (see:http://forum.xda-developers.com/one-...s-hub-t3072773) , will I need to download some other things, or do I just flash the rom thru TWRP?

And if I perhaps want to go back to stock, how do I do that? I didn't know what a nandroid backup was at the time....

Sorry for the probably dumb question but I'm scared ****less about bricking my phone.

Thanks.