Question How to replace graphics card (which screw)

Solution
You have to do nothing with that screws. Those screws fix the bracket to the GPU. If you want to remove the GPU you remove the bracket too. That's how it goes.
The bracket is mounted to the case with one or 2 screws. And you have to unhook the PCI-e bracket clip.
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As above, you need do nothing.
But those brass screws are actually there to secure the dvi cable to the port.
Sometimes, if the brass is not screwed tightly into the card, it will come loose when you unscrew the thumb screw holding the cable to the port.