1) You can open the cartridge and pull out the battery for a short period of time, then put it back in (which isn't easy since the battery is attached to the board).
2) You can open the cartridge and short out the + and - of the battery for a short period of time.
3) This is the easiest since you don't have to open the cart... stick a very small wire in each pin 54 and pin 60, take a AAA battery (probably doesn't have to be, but that's what I tried it with - but make sure it is low voltage, near 1.5V), and touch the wire in pin 54 to "-" on the battery, and pin 60 to "+" on the battery... but don't hold it there, just touch it really quick (there's a chip on the board that gets hot if you hold it there for more than a couple seconds).
Then try the game out, and all the save games / high scores should be cleared... if they aren't, you probably didn't do whichever option you chose long enough or you did it incorrectly.
This is great for those of you that bought games used, and have high scores / save games from the last person that owned it, or just want to start over again. I know this can be useful for Galactic Pinball since that game doesn't have a reset high scores option as far as I know... but there may be other games this might be useful for. Of course I wouldn't do this if there's an option to erase a save game inside the game, but if there's no choice, these will work.
As always, this has never damaged any of my games, but I haven't tested it extensively, so do this at your own risk, and I'm not responsible if this screws up your game.