Here is a link to a parts break down for the Paasche VLS airbrush: http://www.dixieart.com/VLParts.htm
Part 8 is the Head Protecting Cap, is just a slip on(friction fit), just grab it and pull. Once removed you are ready to airbrush. When you are not using the airbrush put it back on, as it protects the head from damage if you drop the airbrush.
If you remove the aircap the airbrush will not function properly.
Assembly 1 is the head assmebly, it includes aircap, aircap body and tip.
The only reason to use the wrench is to remove assembly 1 for cleaning.