Measure the seat of your chair and add three inches to each side, which will allow the fabric to wrap underneath the seat. Choose your fabric and new or replacement padding. The padding should be measured to fit exactly on the seat of the chair.
Turn your chair over and see how the seat is connected to the chair. Most seats are connected with four screws, one in each corner of the chair. Remove the screws with a flat-head screwdriver and lift the seat off the chair. Use the screwdriver to remove the staples holding the old fabric in place. Note how the fabric is folded so that when you put the new fabric on the seat, it will fit on the chair correctly.
Lay out your new fabric and pin the old fabric to the new as a pattern. Cut around the pattern. Mark the measurements of the old padding on the new padding (if you're replacing it), and use your craft knife or box cutter to cut the new padding to size.
Lay your cut fabric on a flat surface with the wrong side facing up. Take your padding and place it in the center of the fabric. Position the seat of the chair on top of the padding. Wrap the fabric over the edges of the padding and the seat.
Staple the top center first and then staple the bottom center and sides. Make sure to pull the fabric tight before stapling each section. Fold the corners the same way that the original corners were folded and staple them down. After all corners are secured, staple the whole way around the seam.
When your fabric is secured, place the seat bottom back on the chair and use your flat-head screwdriver to reattach the screws. You have now given your old chair an updated look.