they can be removed by "floating" spackle or caulking over the lines to smoothe them out. Do not be in too much of a hurry to paint or prime after this process as many of these spackles do shrink and require multiple floats.
Process in order:
wipe down the surface to get it grease and dirt free. putty or caulk in any defects or holes. remove all light plates. apply two or three light coats of Zinser primer. many light coats better than few heavy coats. apply two or three finish coats.
you will be so happy with the outcome, your area will be brighter, cleaner and fresher. Make sure the sheen is NOT flat paint.