Step 1: Remove canvas from the wooden frame using a sharp knife (see below)
Cut on the outside of the staples, loosen and remove canvas. Put it aside and we'll get to the canvas in a minute!
Step 2: Stain the wooden frame with your favorite wood stain color.
My favorite as of now is Special Walnut by Minwax. Allow the frame to dry completely; I'd leave it over night to be sure as you don't want it to bleed onto your canvas!
Keep in mind staining the frame is optional. If you like the look of the bare wood, just use it that way!
If you need a little guidance using wood stain, see my process when I made DIY rustic wood shelves behind my bar.