Well the reason it looks yellow and ugly it was probably finished with an oil based varnish. An oil based varnish yellows as it ages and this one has been around for a while. I would start by stripping the old finish off. I normally use Kleen Strip remover. It's available at the box stores and even walmart. Work on one side at a time. The remover will dry out on you and it's important to keep it wet with the remover for 15-20 minutes and scrape off the old finish and stripper with a broad knife. Then as soon as possible the residue needs to be cleaned off because removers contain wax. You can wash it off with lacquer thinner and rags or if you have a power washer that the pressure is adjustable to under 1500 psi you can rinse the residue off with water. Just don't put the nozzle right on the wood and there will be no damage to the wood or joints. Since the lid has the paper tag, I would probably do that one with lacquer thinner to prevent getting water on the tag. Once you have the finish stripped off I would sand it inside and out and put just a clear finish on the exterior. Cedar is prone to darkening like cherry does. You can slow this process down with a product called Sun Block sold by Kwick Kleen. It's a sun screen formulated for wood. Then for a finish for the exterior you need one that doesn't yellow. You could use any finish that was acrylic. If you have the means of spraying you could finish with a pre-catalyzed lacquer or a water based polyurethane. I would leave the interior unfinished.