Sheila, Bruce is right on. If the finish on your floor really is varnish, so much the better. Paint thinner will attack varnish slowly if at all. My guess is that it is polyurethane and paint thinner will attack it a little but the bumps from the carpet pad have to come off if you want the new carpet to look right and paint thinner is about the mildest product that will do the job. Be sure to do this with all the doors and windows open. Henry