Opti Spark Help

I''m new to this site, But I need some help, I have a 94 cadillac fleetwood. I like to ask you guys how hard is it to replace the opti spark? My car keeps turning off and the auto mechanic said it was the opti spark and rotor cap, I change the rotor cap but didn''t want to go any further cause not sure what to expect. If there is anyone out there that can guide me or show some pics or give me some input, It is just to much to get it done by a shop. thanks alot