Angella: here's an easy (no prep work) product to use!
If you don't want to paint and keep the wood grain look, the easiest way is to strip them down with something like Citristrip, clean them off, give them a light sanding to have a smooth surface and stain them with your choice of stains. When we did ours years ago, we ended up liking the look before the stain went on and we just used poly on them and put them back up in the kitchen once done. We were very happy with the way they turned out. We did ours as a project over the winter and didn't do all of them at once so that we still had a usable kitchen. I liked them much better than if we had painted the cabinets, I loved the wood grain, they just needed to be lighter so you could actually see the beautiful wood.
Purchase a Rustoleum kit for cabinets and you will find everything in the kit that you will need to get the job done. Generally, the kit costs less than $100 and there is enough to do a lot of cabinets. .
Gel Stain from General Finishes is a really great product that sits onto of the existing stain instead of penetrating the wood like regular wood stain. Their website has a ton of information on how to use Gel Stain over existing finishes.
If you don’t go the gel stain route, you could paint them. I painted my kitchen cabinets with milk paint from General Finishes. I only had to lightly hand sand the cabinets to rough up the existing finish. You can see my tutorial here: http://momhomeguide.com/my-painted-kitchen-cabinets-a-year-later/