Quoted from Jimmyd044:Upgraded from L1 to L2 last nite. Unplug the machine to be safe, pull the batteries, replace the chip and that's it. Set new time and date on the menu and customize your setting ( free play, 3 or 5 balls) etc..........
You don't need to pull the batteries. The game is going to factory reset itself anyway because the checksums are different in different revisions of ROMS and leaving the batteries in while you swap ROMs will not cause any problems.