Remove two screws holding the buttons board to the midframe.

Lift the buttons board from the power button end, and release the other end from beneath a retaining tab.

On reassembly, ensure that the right hand end of the buttons board is correctly located under the tab, otherwise the assembly will not fit back in the case.

If required, you can now unsolder and replace any of the buttons. For this, a desoldering pump is most effective.

Replacement 6x6mm tactile buttons are widely available in a range of heights. The 5mm height should fit, but lay a ruler along the tops of all the buttons to check the height before soldering a replacement.