To replace a screen door latch, remove the old or damaged handle by unscrewing it and pulling it off of the door. Insert the new exterior handle, screwing the inside and outside handles together with the mounting screws. Finally, mount the new strike plate, using enclosed shims if necessary. New screen door latches and handles are available at most home improvement or hardware stores.
Replacing a screen door latch is a relatively simple project that typically takes about 10 minutes. First, remove the mounting screws affixing the old handle to the door, and discard the old handle. Measure the distance from the edge of the door to the center of one of the holes from the old screws. This distance is the backset measurement. Purchase a new handle and latch with the same backset measurement, or relocate the 5/16-inch mounting screw holes if necessary.
Assemble the new exterior handle according to the manufacturer's instructions, then slide the spindle through the center mounting hole. Place the interior latch over the protruding spindle, then screw together the interior and exterior handles using the mounting screws. If the old strike plate isn't compatible with the new handle, install a new strike plate by holding it in place with the door closed and securing it to the door jamb with screws.