I haven't done this personally, but I watched someone else change theirs.
As Dan'* illustrated write-up
shows, there are two 13mm bolts behind the pulley. Remove those*, disconnect the fluid lines, and then the whole assembly (pump and reservoir) should just pull off the engine. If you're at this point and can't figure out how to separate the two, post a picture.
* My Chilton'* manual shows an additional mounting bolt near the back of the pump, but I don't believe the Bonneville has that one.