Patio screen doors that are top hung have two rollers or glides that hang off a track attached to the top. They are similar to the closet doors you see in a lot of high rise apartments and condominiums. Pocket doors often work this way too.
The picture below shows a cross section through a typical set of top hung door. This particular one is made by Marvin windows. Manufacturers use a few different methods to connect the upper rollers to the top of the slider. Marvins design uses an upper rail with a flange that sticks up. A 1 inch diameter nylon roller is then riveted to that flange.
Other manufacturers have removeable upper flanges with rollers mounted on them. In my kits, I prefer to mount seperate rollers that use their own brackets. I can adapt these to many different manufacturers of sliding patio panels.
The upper rollers on these types of doors are made of vinyl and will likely be brittle and break easily. Be careful not to jamb the wheels against the patio frame causing them to break. The good thing about the upper rollers is that they can be replaced without having to take the frame apart.
After you have successfully hung the panel in place. Use a flat blade screwdriver beneath the bottom wheels and gently let them snap onto the bottom track. Old nylon wheels break easily. The bottom wheels in these doors are often just spring loaded so you most likely wont need to adjust them. All the rolling and alignment is controlled by the upper wheels.
Slide the door over to the fully closed position and adjust the wheels so that it closes without any gap against the side jamb. Test that it slides slides easily back and forth.