How do I update a large old mirror?

What makes a mirror interesting is what it reflects, not the frame. It's a narrow frame so I'd leave it alone or maybe just paint it black if you have some other black accents in your room. A red lacquer look will make it pop if the other colors in your room can support red. If you have a soft decor, maybe bright white would work. Sponge painting is not an "in" type of painting and will make your frame look dated. For more light in your room, place it on the wall across from a window. A large mirror can also make a room look larger.

Lisa: paint with an interesting, even shocking! color. Or, you can never go wrong with a neutral... beige, white, grey...

Oh, that's a perfect mirror to gold leaf the frame.

Depending on where you plan to hang the mirror I would consider the above replies, but if going in a bathroom or bedroom I would consider glueing beads or pearls on the frame. Something with bling.

I glued shells to mine :)

Chalk paint (because of the minimal prep work) either in an accent color that works in the room it hangs in, or go with black/dark gray or dark brown if you do not want it as a focal point in the room.

You could also find some glass tiles you like and will match your colors. Paint the frame first in a coordinating color then attach your tiles. Along the frames edge so it would actually make the frame look larger.

I like all of these ideas, and all would be simple to do. If I were doing this one, I would paint the frame first, as suggested, in a color that compliments your room's theme or something that pops out from your room but matches. Then I would use a make-up sponge - those triangle ones are good for this - and (put little dabs of various colors of craft paints on a paper plate) dip the sponge into them one at a time or mix them up and dab onto the painted frame. Once you get it shaded and blended as you like, you could then snip artificial flowers and leaves and glue them in the corners (perhaps top left and bottom right) to bring it more three dimensional. Small "critters" or fairies or something could be added in the floral corner as a surprise to someone checking out your handiwork. I like to browse through the dollar aisles or clearance aisles to find little things that work for projects like this without spending a great deal of money. Even tiny toys can be used. Let your imagination run wild. If you don't like it, it is easy to paint over and try again, or even wipe the paint smearing the dabs. Just have fun.

Silver leaf to match the Gray frame here's how to do it videos https://www.youtube.com/results?search_query=DIY+how+to+apply+silverleaf It'll be more upscale fancy but with bling

I had a nice large mirror with gold leaf and it was a bit dated so I got some oil rubbed mahogany spray in the area that has the hammered copper etc. I taped the mirror and took it out on the deck and sprayed the frame. It looks brand new. You could also use hammered copper, I used that on a Bakers Rack and it turned out beautiful.

Paint it a beautiful color that works with your room. If you go with a light color, rub a dark wax into the grooves and wipe away excess. If you paint it a dark color, use white wax and do the same process. This will give dimension to your mirror.