How do you get a visitation order modified in Chicago?

I have sole custody of my child and birth dad has reasonable visitation..(no specifics written in divorce decree).I would like to get a written out plan that he needs to follow so there are less arguments involved about pick up and drop off, and if he don't follow it, then its his loss. But im not sure where i need to start, do i need to speak with a lawyer..also birth dad and son go 6 months without seeing one another (fathers own doing) is that considered abandonment, he doesn't even call or try being involved? any advice is needed, so if any one can point me in the right direction, i would appreciate all the help. Thank You