Remove the vinyl cover from the bar stool by taking out the staples or nails holding the fabric onto the seat with a hammer or screwdriver. Pull off the vinyl in one piece, if possible, to use it as a pattern for the new cover. Lay the old cover on a piece of newspaper and trace around it with a pencil to make a pattern.
Cut a new piece of vinyl or upholstery fabric using the pattern made from the old piece of vinyl. Place the fabric on a sturdy surface, such as a table or floor, so the wrong side is facing upward.
Inspect the padding on the seat to see if it is usable. Remove the padding if there are holes or worn spots, and cut a piece of 1- or 2-inch-thick upholstery foam to the shape of the seat.
Glue the new piece of foam to the bar stool seat with white glue, if applicable. Flip the chair over and set the foam-padded seat in the center of the fabric or vinyl.
Divide the bar stool seat in quarters visually, and tack one section of fabric or vinyl to the bottom of the stool from each quarter using a staple or nail. Flip the stool as you tack to verify the fabric or vinyl remains flat on the seat.
Continue to pull the fabric to the bottom of the bar stool and tack it in place with a staple or nail. Tack the corners as the last step, if the bar stool has a square seat. Fold one side of the corner and secure it with a staple or nail, then repeat on the other side of the nail.
Repeat this process with each bar stool you want to reupholster.