It depends a lot on the structure of the chair, how the upholstery is attached. If cushion covers can be removed. etc. For specific suggestions and links, pictures would help. In general, the old pieces of upholstery can be used for patterns. Take pictures as you take it apart, so you know how to put it back together. Use good quality materials for your work. There some excellent videos on YouTube. I highly recommend Thrftdiving where she has step by step on reupholstering a chair.
here are some ideas:
Hi Phyllis, I hope you can use this link, good luck