For this achievement, you must upgrade any one weapon from the Pack A Punch machine. In order to have access to the Pack A Punch, you must link all three teleporters to the mainframe. I recommend having one person stay at the mainframe and have the others run around to the link teleporters to get the clock started. Once you have all three teleporters linked to the mainframe the Pack A Punch will be available. To upgrade a weapon, walk up to the Pack A Punch and press and hold . It costs 5000 points to upgrade a weapon. It is pricey, but it is well worth your money.