1. do a nandroid
2.put firmware in sd root, flash firmware
4.close after 5 min.
5.take out ur sd, and mount to pc
6.delete that firmware and copy the new rom.
7. restore nandroid.
8.start mobile. wait 5 min. thn go to recovery again
8.wipe cach and dalvik flash the new rom. and u r done.
i hope u dont have anymore question