In mid-match press all the function keys from left to right 'F1' to 'F10' until an S12 or S14 appears at the top of the screen. You should now be able to substitute one of your players for your opponent's goalie. If you do it again, you should be able to score - no problem. This substituted goalie is usually pretty useless. Substitute the opposing goalkeeper twice and he will not save your shots.