Remove staples and upholstery tacks from the sofa with a pair of needle-nose pliers.
Remove the leather fabric and batting, being careful not to rip the fabric as it will be used as a template for the new cover.
Lay the old cover on top of a piece of new fabric and cut around the edges with a pair of leather shears, leaving 2 to 3 inches of overhang on all sides.
Insert new batting into the seats, backs and arms of the sofa. Tack it down with a mallet.
Lay the sofa's back fabric over the backing of the sofa. Tuck the fabric into the sides and pull through the opening. Tuck the fabric in tightly and staple the fabric into the wood frame.
Lay the fabric over the seats of the sofa. Tuck in the fabric taut under the sofa's frame. Pleat and staple down.
Lay the fabric over the chair's arms and fold the fabric close to the chair's back, one-third of the way forward. Cut a slit in the center of the folded fabric to the end of the fold. Wrap the ends around the arms and staple.
Reinforce the arms with welting is desired.