It depends on the game and if there is an option for dipswitch settings or not. If there is the option when you press "Tab" to bring up the menu you will see a menu for dipswitch right away then you just go in there and turn service mode on and restart the game. When the game loads up again it should take you into a menu to change different settings. Find and change the one for freeplay, restart the game, re enter the dipswitch service menu and turn off service mode again.
If there is no dipswitch option in the "Tab" menu pressing "F2" (default key) should take into service mode for the machine and you can change settings in there. If "F2" doesn't work look in the "Tab" menu > Input (general) > Other Controls. You should find a setting called "Service".
This really is something that is game to game and rarely will you find games be the same or even all of them having this feature.