those parts are riveted. they are connected using rivets. to remove them rivets need to use small nails and drill.

here's what you'll need.

to remove the rivets
-small nail - one/two only just to whack the small holes on the rivets.
-hand drill, goes for around rm20. electric drill, better but cost a lot more.
-3mm drill bit, look for the short ones if available.

to rivet your case back
-riveter, rm16 at carrefour
-rivet nails. normal or countersunk head rivets.

for instructions, head on to youtube and search 'popping rivets'/'remove rivets'.