You should plan to enter from Yucca Road, the entrance road with signs (near the school bus terminal parking:

As you come up the Entrance, you will see a guard booth.  Keep right to go into the Lower Parking Lot (plenty of parking, a set of stairs to climb to upper level) or keep left and go around and right of the booth to the upper lot (only a few parking spaces, but handicapped and drop-off available).

Once parked, you head right over to the theater.

When you leave the parking lots, you go RIGHT but then KEEP LEFT.  Do not take the two rightmost lanes, they will take you to a locked gate at the Siringo exit.