There should be a bunch of tiny little screws on the backplate holding it to the PCB, there will also be 4 big screws on the back holding the cooler to the GPU die. DON'T REMOVE THOSE. Also don't paint anything near the PCB, if you want to change the color of the backplate then completely remove it. Also, if there are any thermal pads between the backplate and the PCB, leave them where they are and don't paint them