Once stained dark, can you sand and stain to a lighter shade or will it always be pretty dark?
Sanding can be a good way to remove the existing dark wood stain. This will bring up new wood without any stain. make sure to fully sand all surfaces thoroughly and end the sanding with a fine grit to reduce the size of the surface scratches.
Sanding is one option. Depending on the amount and type of wood you could also use a paint stripper to lift some of the stain. If you choose this option make sure the paint stripper says it will also lift wood stain. Most likely you will have to do some sanding after stripping but it could save some time.