I wouldn't touch this room. Right now it actually feels like a den. All warm and cozy. If you want it to feel cheap like a cookie cutter house then go ahead and start going crazy with a paint brush.

I would change your furniture for lighter ones and then find a nice area rug. Then your all good to go.

Please post a picture of the other end of the room. Right now the layout doesn't work for watching TV. I would remove the corner cabinet.

The room is brown because almost everything in it IS some version of medium brown...and some of it seems slightly pink-brown.
You could leave the rock wall if it is natural, paint the beams a dark brown, paint the walls a non-brown, change the carpet to a non-brown, and bring in some colored upholstered furniture. If the rock wall has been painted, you could remove some paint in an inconspicuous spot to see the natural color and decide at that point if the natural color is a good one.

I am not sure the purpose of the corner cabinet. Maybe it could be painted or removed.
I would update the satin gold fireplace screen thing.
I would consider getting rid of the tile floor and/or add a friendly warm rug.
The furniture is pretty dark. Lots of darkness going on. The fireplace and windows are actually great and interesting to me overall.
In this picture the furniture seems oddly placed and lots of big rectangle or square pieces. What is the focal point of the room? Fireplace/tv, windows??? Not a big fan of huge TVs above the fireplace scheme, but it’s your house, not mine!
Add some different textures - rug, throw, pillows, etc for interest and color.
Imagine if the room was empty what would you like the focal point to be and what practical layout do you need.

Also, updating the furniture to more Mid-Century modern might give you some smaller pieces to work with- not sure if they fit your “contemporary” style, but I think you could update the furniture and highlight the room better and your style better.