REPLACE SCREEN DOOR ROLLER

First back off the top adjusting screws on the screen door, so you can lift the sliding screen door out of the door frame. With the screen door removed, look on the end of the screen door where the wheels come out. You will see a small attaching screw holding the wheel to the door frame. Remove the old wheel and install the new wheel. Check all wheels and replace the screen door on the track by putting the top of the screen door in the upper channel track and then sliding the bottom of the screen door over the bottom track. Sometimes you need a tool like a flat putty knife to lift the bottom screen door wheels over the bottom track. With the door on the track, first adjust the lower wheels to square up the door and slide smoothly, then adjust the top wheels just enough to keep the door from jumping off of the track.

Something tells me you may have what is called a "corner wheel." If so, you must take the door apart in order to remove the complete corner with the attached wheel. If you can, upload a few photos of your hardware so we can help you identify it.