the only ROM available for the Sm-G900H is something called xtrestolite. First you have to update the boot loader (easy) and update the modem (easy still, not dangerous) with Odin. Then you just back up your phone and flash the ROM with CWM. Super easy, no features but stock (very very bare) touchwiz and pre rooted. It also comes odexed so android runtime works FLAWLESSLY. Best ROM you can get for this phone.