Squeeze the two optical drive bracket ears together while pulling the drive up toward yourself.

It may be helpful to hold the logic board down near the optical drive connector when pulling the drive toward yourself to avoid both components lifting together.

Pull the optical drive away from the side of the rear case and remove it from the iMac.

If your optical drive is particularly stubborn to remove, try the method used in the optical drive guide from the A1144 G5 iMac.