copy the rom zip file in memory card and insert into phone.
Take out battery and insert again.
Hold vol Down button and press power button.
phone will boot in recovery mode.
select recovery, now phone will reboot in recovery.
select install zip from sd card, then select zip file to install.
Select the rom file from the list of files in the card.
make sure the phone is charged properly.
It will take some time.; after it's finished reboot the phone.
Phone should work fine.