Don’t necessarily migrate to the new instance; create a temporary instance, restore onto it, check it all works OK, then create a new container in the original location, shut down the old one, and restore the upgraded backup. Not that that should be any different, functionally, to doing an in-place upgrade, but at least you won’t blow up the live site if things don’t go according to plan (which, given how old that instance is, I wouldn’t rule out).