Remove the leather cushions from the couch. Locate the seams of the cushioning and use a seam ripper to remove the seams of the leather.
Place the old upholstery flat on the new leather upholstery. Lightly trace out -- an inch larger from the old fabric -- the pattern of the old upholstery on the new one with a marking pen.
Cut out the pattern on the new leather with scissors.
Place the old stripped cushioning into the new leather upholstery. Arrange the leather to cover the cushioning. Pin down the arrangement with sewing pins, leaving 2 inches between each pin.
Sew the leather with a thread and needle. Use thread that matches the color of the fabric.