How can I easily and inexpensivly update a large frame?

paint the frame, get a new matt cut

How about sanding the edges for a shabby look?

Video: Refurbishing Picture Frames | Martha Stewart

www.marthastewart.com/913077/refurbishing-picture-frames

Use some tacks with the rounded tops (carpenters tac's?) Tap them into the wood frame all around the thickest part. If you cant tap them in you can cut off the point end (with wire cutters) and glue the heads onto frame with a glue gun or other glue. (sometime the glue gun glue will not hold the metal tacs v well) Pick out some flat paint in a color you want and paint the whole shabang ! Use a damp cloth and just wipe off the paint from the tac heads with long strokes. If you take too much paint off, you can dab more on and wipe again. The silver or gold tone tacs you use should show most of their orig tone after wiping off the paint. If you use white paint you will get a shabby chic look. If you want more depth to the look, add some dabs of brown or any color to the tac areas using a paint brush with a pouncing motion( the brown paint will go into the wood areas between the tacks as well as the tops and this is ok) then wipe away some of that color off the tac heads as well....just keep dabbing paint until you get the color tone you want...If you goof up, just repaint the first color again and wipe away! If you dont like the whole project just paint the wole frame a solid color! good luck

You can try removing the print and the glass from the frame (if there is any) and painting the frame however you choose just make sure that you put several thin coats letting it dry in between coats if you're going to use spray paint.

Affix some accents to the frame and or paint it or add crown molding...