1. The leg being a part of the frame assembly using wooden dowels, wood corner blocks, and glue with screws
Discussion here will be limited to item #2, as #1 requires various woodworking skills found at a furniture repair shop.
Only 1 bolt and tee-nut kit is required for any leg quantity.
Grasp leg and twist counter clockwise. It will remove.
You can make certain the bolt is 5/16" and not metric (which almost measures 5/16" but has a different quantity of threads per inch), by trial installing a known 5/16" nut onto the leg. A trip to the hardware store with the leg can save a lot of frustration. If the bolt is 5/16", so is the tee-nut.
Installation is the reverse of removal. That is, grasp the replacement leg and turn it clockwise until flush tightened against the frame. A leg that is not flush against the frame is weak.
If the original leg has a dowel screw (a screw that has a point at both ends) and screws into the frame, it is suggested to install the replacement leg with a dowel screw again (How to remove a leg bolt). A tee-nut could be installed so that a bolt could be used, but it is difficult to access on items that are already upholstered. Never-the-less, if that is wanted, call our technical department for instruction.
Related leg item hyperlinks: