Remove the chair seat cover. Flip the chair over and remove the staples holding the material down underneath the chair. Carefully pull the material out of the corners, ensuring you don't tear it.
Flip the chair over, standing it up, and gently pull the material up off the seat of the chair. This will expose the foam underneath. Use a large rubber band or some twine to wrap around the material and secure it to the top of the chair so it's out of the way.
Remove the foam, which is glued to the chair. Using your fingers, move up along the foam on the sides of the chair until it's all removed. Do this slowly to avoid damaging the foam if possible. Lift the foam up and secure it to the back of the chair along with the material.
Remove the piece of inner foam which is likely well-worn and throw it away. Leave the original webbing in place because it will provide additional support along with your new webbing.
Lay a piece of webbing vertically across the chair from the front to the back, beginning in the middle. Tuck it up underneath the foam and the material on the back, ensuring it's secure. Staple it to the back, being careful not to get too close to the back of the chair.
Pull the strap tight and staple the front, keeping staples away from the edge. Add straps vertically about 2 inches apart until you've covered the chair vertically, stapling each at the back first and then the front. Trim excess webbing.
Put the horizontal webbing in, beginning in the middle of the chair, interlacing it with the vertical webbing. Staple it on one side and pull it tight to the other side and staple it. Continue adding your vertical webbing, spacing them 2 inches apart until the chair is covered horizontally. Trim excess webbing.
Lay a new piece of inner foam on top of the new webbing. Stuff it in so that it fits under the original foam. Pull the original foam back down and staple it all the way around the chair on the sides. It only takes about three or four staples on each side to secure it.
Pull the fabric back down, adjusting the foam underneath to make it smooth. Pull the fabric to the corner and pull it down. Carefully stretch the fabric and pull it over the remaining corner. Smooth the fabric down.
Pull the front material down so it is even. Tuck the material up underneath the bottom of the chair and staple it. Flip the chair over and add staples. If you want the bottom to look finished, you can staple a piece of material across it to hide the webbing underneath.