Quoted from KevInBuffalo:
Take off the legs and fold the head down. Bring a pillow or something to go between the head and the body of the machine. Definitely cover it and strap it down.
First off, congrats...Firepower is a cool game. Just to reiterate what others have said...take the legs off and take the balls out.
Secondly, I'm not sure that Firepower has a hinged backbox. If it does, definitely fold it down. If not, you'll have to decide between:
1) Leaving the backbox on. Probably ok, just make sure all the backbox bolts are there and securely installed and the whole game is covered with your tarp or moving blankets. Push the game up to the front of the pickup box with the coin door facing the tailgate.
2) Removing the backbox. This is what I always do, but it involves unplugging all of the connectors from the boards in the backbox. If you do this and this is your first time, make sure you take lots of pictures and/or label connectors to make sure you can get it plugged back in the right way. I think this is the safest of all options.
3) Removing the backbox bolts and strapping the backbox to the cabinet (leaving all of the connectors connected). I know people do this to save time plugging things back in, but I don't like the idea of the backbox slipping and putting strain on the connectors and board header pins in the backbox. I, personally, would stick with options 1 or 2.