Remove original chair cushion using a screwdriver. Put the screws in a safe place.
Lay fabric on a flat surface with the front of the fabric facing down. Place the chair cushion upside down on the fabric.
Trim the fabric to a size that will wrap around the cushion.
Wrap the fabric around the cushion and staple the fabric to the underside cushion. Trim extra fabric off with scissors.
Re-attach the cushion to the chair base.