Painting the walls would be the easiest way. Start be cleaning the walls with TSP (tri-sodium phosphate or TSP substitute) or Dawn, then use a couple coats of primer followed by the paint of your choice! I hope this helps!
Jen...You can clean well, prime then paint. I did in my basement and love it.
Clean, sand, wipe down, prime and paint.
You can clean with TsP, then prime and paint. I did my daughter's bedroom about 18 years ago and it still looks great except the dings where she bumped her bed on the wall.