There are five screws to undo - one in the bottom centre (just above the two smaller holes), and four underneath the rubber feet. You will need to peel the feet off the case to access these - mine were so aged and stiffened they crumbled apart when I tried. You can optionally replace these later with new rubber feet up to 14mm in diameter.

Push down hard when starting to loosen each a screw. They have been set in hard, cheap plastic for possibly decades, and may take some force to start moving.