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What are you wanting to do with it? You could paint over the stain.
Sand with a hand sander in circular motion untill it is down to bare wood. Pay close attention to the walls. Many times they don't get sanded there properly. Vacuum the floor thoughly to remove sawdust. Stain and then use 3 coats of clear.
Clean the paneling as clean as possible. If you find it is actually laminate, sand the thin layer off and clean again. If you find plywood (MDF?), sand off the stain, then clean the sawdust out of the grooves. The wood may have some textures because of variations in the wood used as well as the stain and finish used. You generally cannot go from light to dark stain, but if you sanded out the stain level to the wood beneath, you can probably go with light stain or paint in any color. Best wishes! 😊