Could anyone tell me how to remove old finish off?  Thanks.

There have been a lot of threads discussing this. The first general rule is avoid using chemical strippers, as they can soften the glued laminations, etc. The Golden Sovereign Division of Ben Pearson was their premium line and those bows came from the factory with mighty good finishes over that first quality rosewood and ebonite. The embossed plastic caps over the mercury capsules may be able to be gently pried loose  as that area is the first to display finish breakdown...lacquer doesn't like to stick to plastic as well as it sticks to wood. Otherwise, protect those with masking tape. The most popular approaches  with trad bows are to start with a cabinet scraper or equivalent ( I use a dull pocket knife with a mostly straight blade) and scrape the original finish off, always working from center of the riser toward the tips, never with the blade held at an acute angle as that can dig in ,especially on the edges of the limbs. The alternative method is starting with 240 grit sandpaper and hand -sanding with progressively finer grits. Be especially careful working over the serial number , etc., as preserving that original writing is preferred to sanding it off then re-writing it yourself ( take some up close photos before you start, just in case). Also, if your original finish is mostly intact, all that may be required is a light sanding on the existing finish to polish it up, starting with 320 grit and moving quickly to 440, 600,then clear coat with a wipe on or spray finish.

Sorry I did not make it clear in my question.  I already sand the whole bow except the brass area as shown in the pic.  I tried some metal polish compound without success.

Are those caps brass or plastic?