How to reset to defauft?

Mar 18, 2013
Hi all,
I'm currently using ROM of muiuiandroid, multilanguage, installed many apps. It's make my Mi2 run slowly. Now I just want to run ROM with English only, choose carefully what apps I need. Please someone help me, I dont know how to reset it! THank you very much.
PS: I'm just use this phone for games, 3G Network, so dont care anything about contacts, calender, etc...