1999 Convertible Mustang Detonation

Hey guys I'm new on the forum, but I've loomed at alot of stuff people post. I'm pretty sure I have a detonation problem in my car. It also shakes when I accelerate not terrible, but you can feel it. It sounds like a ball rolling on my dash when I accelerate and I started using a higher octane fuel from she'll and it doesn't seem to help. I have no clue how to adjust my timing lol no idea whatsoever. I want to figure this out so I still have my baby for a while. Please help Thanks guys!
 
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