How do I disassemble this shower screen without damaging it?
It is difficult to be certain, but removal of the screws at the top corners should allow the top crossbar to be removed. There may be other screws that join the sections of the frame, or once the top bar is removed, the side panels may be able to slide out. The tracks against the wall are probably held in by screws hidden under the side panels.

To get to a screw in a tight space like the top corner, you can use an offset screwdriver



You need to be careful in removing the panels. They may be heavy, and significant flexing may lead to breakage.

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