Question: I have to remove these rivets (see pics).

What tool can I use for that?

[![enter image description here](https://i.stack.imgur.com/qtA2F.jpg)](https://i.stack.imgur.com/qtA2F.jpg)

[![enter image description here](https://i.stack.imgur.com/pFaAr.jpg)](https://i.stack.imgur.com/pFaAr.jpg)

[![enter image description here](https://i.stack.imgur.com/Pazxk.jpg)](https://i.stack.imgur.com/Pazxk.jpg)

Answer: 
Those are [rivets](https://en.wikipedia.org/wiki/Rivet) (specifically pop-rivets), they are a permanent fastener not intended to be easily or routinely disassembled and reassembled.

[![enter image description here](https://i.stack.imgur.com/ANWmg.jpg)](https://i.stack.imgur.com/ANWmg.jpg)

There are many ways to remove them

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

Grind
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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
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Some people say they chop off the heads using a chisel and hammer. I guess they mean a [cold-chisel](https://en.wikipedia.org/wiki/Chisel#Cold_chisel) of the type intended for use on metal, not the type of chisel intended to be used on wood.
I always drill. Works like a charm, rivet's metal is quite soft.
On the third picture, rivet et gone already, you should be able to push it out.