Below the nob a piece of plastic
Below the plastic the leather
You need to take a fat screw driver or butter knife and insert it between the plastic piece and the nob and twist. Don't try using a jewelers screwdriver or something sharp as you may mark up the plastic piece. The plastic piece will separate from the nob slowly - as in it won't pop off. Anyways, after you have separated the plastic piece (which is attached to the leather) from the nob.... just unscrew the nob. The nob does unscrew so don't try to just lift up.
PS. You may have already removed the plastic (and leather) from the nob - I just wanted to be specific for everyone. The first time, I had to wrap the nob with a old sock and use a plumbers wrench to break loose the nob as it was tightened beyond my strength.