OK, this is pretty easy, and as I said, fairly intuitive....
Once you have your flight plan loaded into the 530, go to the flight plan page, turn on your curser, scroll to the waypoint you want to delete ('highlight' it), then hit the CLR (for clear) button, and the unit will ask if you want to delete that waypoint from the plan, the YES selection will be blinking, then hit ENT (enter). Your waypiont is now deleted from your plan. If you decide you don't want to delete it, instead of YES, use the 'outer' navigation knob and highlight NO, and hit ENT.
Now, you are not deleting the airport from the database, but simply removing it from the flight plan. You cannot delete the airport from the database itself.