ONLY work on the inside with the power off, not only because of possible electrocution, but the lazers can damage your eyes.
Open the drawer, switch off the power.Remove the cover.
You should see two shiny rods with a mechanism that can slide from the middle of the CD towards the back. You may be able to see a screw mechanism on the side. The mechanism should slide freely backwards and forwards. the slides and the screw mechanism should have a small amount of silicon grease to lubricate them.
Note CDs play from the middle outwards, the opposite of records. Usually you just need to clean and lightly apply a little SILICON grease.
Frank Caves, June 2010