Remove all of the old fabric from the chair. Try to do this while keeping it intact. You will need the measurements for the new fabric. Measure the chair and old fabric to determine how much fabric you will need to upholster the sofa chair. You will need one piece long enough to cover the seat bottom and front bottom of the chair, one for each arm and for each side of the chair, one for the top front of the sofa back and one for the sofa back. You will also need one for the sofa seat. Cut the fabric out.
Take the piece of fabric for the seat bottom and drape over the sofa bottom. Leave the ends hanging off the front of the chair. Tuck the edges neatly into the sides of the sofa bottom and staple into place. Pull the fabric tight under the bottom of the chair and staple into place.
Place some batting over the arms of the chair. Lay the fabric for the arms over each arm one at a time. Tuck the edge of the fabric into the inside bottom of the chair and staple into place. Pull tight over the arm and staple into place. If the chair arm is rounded, you will need to make pleats in the fabric so that it has a neat appearance. Use a butter knife to create the pleats and staple into place. Pull the rest of the fabric tight over the side of the chair and staple under the side of the chair.
Lay the fabric for the front back of the chair over the back of the chair and tuck the corners around the sides of the back of the chair. Pull tight and staple along all edges.
Take the fabric for the back of the chair and lay against the chair back over the front of the chair. Leave about 4 inches hanging over the back of the chair. Staple into place. Staple the chipboard along the remaining 3 edges of the chair back. Pull the fabric back over the back of the chair. Take the side pieces and stick the upholstery tack strip through the fabric from underneath. Turn the strip over so that the unfinished edge of the fabric is hidden and tack the strip to the chipboard. Do the same for the other two sides.
Sew the fabric into a new seat cushion using the old seat cushion as a pattern. Put the old seat cushion into the new case.
Look over the chair to see if you have any staples showing. If so, you can hide them with buttons or some other decorative item.