How to remove rivets?
Those are rivets (specifically pop-rivets), they are a permanent fastener not intended to be easily or routinely disassembled and reassembled.



There are many ways to remove them

Drill

You can drill them out with a HSS drill bit of appropriate diameter for the stem of the rivet. Once you have drilled out the centre, the heads will fall out.

Punch

You may be able to punch out the center using a hammer and a suitably sized punch.

Grind

You can grind off the head using an angle grinder or something similar. Once the head is removed, the remainder will fall out or can easily be pushed out.

Chisel

Some people say they chop off the heads using a chisel and hammer. I guess they mean a cold-chisel of the type intended for use on metal, not the type of chisel intended to be used on wood.