How to replace a 1997 geo prizm lock?

If you mean the door lock cylinder...remove the interior door panel. On the back of the door handle there are 2 10mm hex bolts. To the outer edge of the door there is an access hole. With an extension, remove the 10mm bolt that holds the lock cylinder and door handle together. Reach in and push the nylon retainer that holds the rod into the cylinder (yellow on driver side, white on passenger side) and remove it. A slight twist of the cylinder will remove it from the door handle. Replace in reverse order.