No
You may not get the new stuff spawning in where you have already explored though.

I would advise if you care about the leveling and progression that you start over. If you don't care then don't bother and just carry on with whatever.

I have a few worlds going I will "upgrade" with new stuff but to check out new systems being put in I am starting a new world with a new character for the update.

But you won't Have to start a new world and old worlds will still function.

edit add - and yes this has been asked way too many times already. People should really learn to use the search function.