What may cause raised lines on drywall?
Those are almost certainly seams between sheets of drywall that are either settling or have suffered moisture damage. (By far the most likely is settling, but since there's a window above, I wouldn't rule out moisture.)

Check the exterior and interior on the window above to see if there's any evidence of leakage.

Otherwise, you could re-tape, texture, and paint, but that's a lot of time for not a lot of benefit.