I have tried changing it. I can seem to set maximum credits, but cant change any values. Not a biggy, will continue trying to understand the set up, seems a little too old school for me  :)

I am assuming your talking about the switches on the CPU board? Will mess around with it on the weekend.

use the button inside the coin door

Set the AUTO-UP/MANUAL-DOWN switch to AUTO-UP and depress the advance button until the number 18 is in the match display. then press the start button until the number in the score display goes to 0