Turn the stool over so the legs are facing up. Notice the staples holding the current fabric in place.
Wedge the tip of a flathead screwdriver underneath any staples and pull up to remove them.
Take off the fabric and place it flat on a work surface.
Remove the batting, if necessary, the same way you removed the fabric.
Measure the old fabric with measuring tape. Write down the length and width.
Cut the new fabric and batting (if applicable) the same width and length as the old fabric using fabric scissors.
Turn the stool right side up. Center the new batting over the seat of the stool and center the fabric over it.
Turn the stool upside down again, holding the batting and fabric in place.
Fold the ends of the batting and fabric underneath the seat of the stool. Staple the sides of each into the seat with a staple gun.