In general you need to keep heading uphill and don't take any left turns. On leaving the roundabout you'll first see a sign to the health centre (centro de salud) to your left. The next road to your left is C/Sorolla. Straight ahead is the Almijara 1 urbanisation - don't go into there, your road curves to the right. You'll next pass a beauty centre (centro de belleza) on your right. Keep going up the hill and you are approaching the los poetas barrio where all the streets are named after famous? Spanish poets. You pass C/Candal on your right. You then come to a junction with a right turn (C/Damaso Alonzo), a left fork, and straight ahead, the road you want continuing up the hill. You pass C/Rafael Alberti on the right. You then come to a baker (panaderia) on your right. Keep going up the hill passing a couple of electricity pylons on your left to the point where the road ahead is marked up as a cul-de-sac. You take the road to the right and you'll find the entrance to San Juan de Capistrano on your left.
This sounds more complicated than it is - essentially you just stay on the main road. If there are any locals about they'll know where San Juan de Capistrano is (pronounce "Juan" as "whan")