painting and changing of color fabrics are going to be the cheapiest ways of modernizing the room. Sorry you can't comprehend that.
Painting is the big one......you want to pick a color that you can live with everyday, maybe you want it light...make the room bigger, or darker to make it more cozy or romantic.
After that you pick the curtains, rods, and bedding to match........the headboard is always important in the room's design. Lamps....ceiling fan etc.
I have paintings up in my master... they go with the room's decor. I'm still working on every room in my house but those are your cheapiest fixes, although they can still get expensive.