Is that an old laptop? I just bought a new acer laptop 4 days ago and the first thing I did was change the dvd/cd-rw drive to a dvd-r drive.
Anyway, under my laptop, I took out a screw, pulled out drive. That's it.
Good luck
Usually there is only one or two screws that need to come out to be able to remove the cd drive. One almost at the very back of the drive (towards middle of laptop) and maybe one by the front. When all else fails just start unscrewing and you'll get it eventually.