My dream phone just now. may i know about the battery perfomance? smooth playing any games?

Hello guys i need some help from u, i'm new to desire, yesterday i bought 2nd hand phone from someone from lyn but the phone already root, the problem now is i cant use market because google account still his acc so i hard reset the phone but appear something like clockworkmod, i dunno what is this then i choose reboot now but still same his google account still there. so i cant use my google acc to use market.. any help? how to unroot? i dunno where to start.

Hope someone can help. teach me step by step how to back to normal desire (unroot)