Your header says stain, your question says refinish, which is it?? If previously finished(poly or other), the old finish needs to be removed and the wood sanded as prep for stain. To simply refinish, lightly sand the finish and apply new finish.
Minwax makes a colored finish called Polyshades, available at home, hardware, paint stores. I am not a big fan of it because if you get runs or the finish pools, it will be darker and obvious. It does eliminate the need to strip the old finish, just sand lightly.