Measure a piece of scrap wood to the length you want to remove from the chairs and cut it to size using the tenon saw. If your chairs are angled at the bottom, measure the angle with a protractor and cut the top and bottom of the scrap wood pattern to the same angle. If only the front or back legs are angled, cut two different patterns.
Place the scrap wood pattern against one of the chair's legs so that the bottom of the pattern is flush with the bottom of the chair leg. Mark the chair leg where it meets the top of the pattern using a sharp pencil. Repeat this process for all of the chair legs.
Cut off each of the chair legs at the marked points using the tenon saw.
Sand the rough edges of the chair legs with 60-grit sandpaper. Sit in the chair to ensure all the legs are even, with no wobbling.
Stain or paint the cut edges of the chair to match the original finish. Seal the paint or stain with varnish if necessary. If the chair is unfinished, place floor protectors on each leg to extend the life of the legs and prevent floor scratches.