Upgrade watch
If my watch is paid off and not charging right can I upgrade to a 5 with no issues??
Question marked as
Not for free, if that's what you are asking.
You can trade in the watch and use whatever Apple will give you for it to cover part of the cost of the new watch.
If it has an issue, its value may decrease from what Apple may normally give for a fully functioning watch.
See here to get an estimate: Apple Trade In - Apple