Shower doors are meant to give you privacy and keep the water inside the shower. Over time the shower door begins to stick and becomes difficult to operate. This is usually due to normal use. Preventing a shower door from sticking is a bit different than most doors. The shower door uses brackets inside the door frame to level the frame sides. Sometimes these come out of adjustment causing the frame to sag just enough to cause problems. Fortunately this is a minor adjustment that does not require door or hinge removal.
Open the shower door so you can access all of the shower door frame corner screws. There is a corner bracket brace inside each corner of the door frame.
Loosen the screws at each corner of the shower door frame with a Phillips-head screwdriver. You only need to loosen the screws two full turns. There are two screws at each corner edge. Do not loosen the hinge screws. Loosen the two screw on the inside door handle two full turns.
Stand a 1-foot tall block of wood under the outside bottom edge of the shower door, 6-inches from the outside edge of the door. Place shims on top of the block and under the door. Ask a helper to hold the door steady while you add shims between the door and block of wood.
Hold a black of wood against the bottom edge corner of the shower door. Tap the bottom of the wood a couple of times with a hammer. This begins to straighten the door frame against the inner corner brackets. Drive in the shims once you tap the bottom of the wood.
Tighten the corner screws and the door handle screws with the Phillips-head screwdriver. Remove the block of wood and shims. Close the shower door and test the operation. Repeat adjustments if necessary.