Pre-v8 to v8.x Upgrade Process (Cloud)

Thank you.

I reviewed all of the above info and still can't seem to figure out the Sync up process. Our CSM provided info but hoping I would get exact steps and the nuances from someone who did the upgrade. 

Who and how would we do the sync up between active/current and v8 instances is the question that is bothering me and I think that is what decides the timeline.