The following thread might help a little:
What do I need to do to get ready for Sept 30?
But mostly it’s just going to be a lot of individual research to figure out what you want to do for each aspect of what you have. Nothing is exactly “seamless and easy,“ unfortunately. One option is just to sit and wait and see what breaks, because some things will be automatically migrated for you. And then one by one fix whatever got broken. i’m not saying that’s a good option, I’m just saying that’s what some people are choosing to do.
If you want to be more proactive, again see the link I just gave you.