You have two choices about how to accomplish this new look, either strip off the finish then apply a stain or apply a gel stain over the existing finish.
I will explain how to apply a gel stain over the existing finish for a new look. This method is more efficient and in some respects easier to accomplish. But, it can only be used to darken prefinished cabinets not lighten them.
At this point it is a good idea to practice before committing to the whole job, especially if this is an entire kitchen. It took me a couple of practice runs before I felt comfortable re-staining cabinets using this method. I practiced on the back of a door and it isn't easy and will take a little finesse. If you don't like the results you can easily remove the stain with mineral spirits (paint thinner) and a clean rag. Keep practicing until you are happy and comfortable with the results.
Oh remember to remove the doors and drawer fronts it's much easier to prepare and re-stain cabinets if the doors are removed and refinished in a horizontal position. If the drawer fronts are removable now is a good time. The entire cabinet frame can be exposed with all these pieces removed. Cover any items inside the cabinets with light weight plastic this will keep the sanding dust from getting on dishes.
Now you’re ready to clean all surfaces to be gel stained.A surface free of grease, soap scum and other contaminates will help make sure your new stain and finish stick for the long haul. A strong cleanser can be used. I like TSP (trisodium phosphate) which is also available in a friendlier no rinse formula. You can also use a scrub pad on heavy deposits. Allow to completely dry before continuing to the next step.
After cleaning your ready for sanding this step will de-gloss and roughen the surface so the gel stain will stick. Hand sanding is the best method. A palm sander is a bit too aggressive. A combination of sandpaper and sanding sponges will work great. Use 150-180 grit for the paper and fine sanding sponges. If you have any peeling clear finish use 120 grit sandpaper to remove anything that is loose then finish with 150 grit to blend the damaged areas. The idea is to produce an even haze after sanding. Try not to remove any finish or stain. After sanding remove the fine dust with a shop vac and tack cloths and yes clean again this step isn't absolutely necessary but a good idea. I like to do one more final cleaning to remove anything that might be present and get rid of any remaining dust. For this I use a surface de-glosser. My favorite is Paso Liquid Sander. It is a very potent chemical that has a strong smell, but does a great job.
Use clean white rags saturated with Paso and wipe every surface. It's a good idea to aggressively ventilate during this operation. Allow the surface to dry for 1 hour before applying the stain this is by far the hardest part. Using gel stain to re-stain cabinets with an existing finish requires a light consistent use of the brush and a little artistic flare. The gel stain I like and highly recommend is Old Master Gel Stain. I have found that it is the easiest to use. To apply the gel stain you will need a very high quality white china bristle brush (1-1/2—2’&rsquo
and a few clean white rags.
Now apply the stain in the same direction as the wood grain and apply in thin coats. You can always apply another coat after 24 hours for a darker color. Use quick short strokes of the brush in one direction only. Pull the brush towards you, reach out and pull toward you and so on. This way you are brushing in only one direction, not back and forth.
Use a small amount of stain and start applying an inch or so away from the last stained area. Use a rag to remove excess stain from the brush with a dabbing motion. To blend one area into another remove the excess stain from the brush and use short quick brush strokes to pull the excess stain away from the thick area. This is why it takes some practice. Now the stain must dry for a minimum of 24 hours before a clear wood finish can be applied. Any good finish can be used; including acrylic urethane, water based polyurethane, regular polyurethane and spar varnish. Two coats are needed with a light wiping of a cleantack rag between the coats. A very careful and light sanding with a worn fine sanding sponge is necessary if dust settles on the fresh finish.
Now if you follow what I did by using this method to re-stain cabinets for a new darker color is a doable project for many. But, getting a consistent look with the gel stain isn't easy. You will have to practice until the brushing method mentioned above feels natural. It's easier to apply the stain when all of the preparation is accomplished. This prepped surface, cleaned and sanded, grabs hold of the stain allowing an easier time with blending.
After the final coat of finish is applied allow a few days for proper curing and hardening. You can still use your cabinets, just be careful not to damage the stain or finish and leave the doors open. This way nothing has a chance to stick and cause damage.