If the release knob does not work and you can not get your lens off you will have to take the adapter apart. 

Three Screws need to be removed you should use a 000 Philips screwdriver or a jewelers Philips screwdriver. Make sure not to strip the screws.  

Once the screws have been removed pull the top cover off the lens mount ring

as shown below.

Once the top is removed you will need to take a small screwdriver and lift the pin 

as shown to release the pin from the lens now you can twist the ring off of the lens 

and  remove it.

This is how to remove the adapter when the release mechanics doesn't work.