You can also get this mod from ThunderStore. For those allergic to Nexus. ;)

https://valheim.thunderstore.io/package/JereKuusela/Upgrade_World/

It is really, really good and very exhaustive, but requires some extensive reading. Don't worry, you can't break stuff unless you really want it.

It can completely reset your entire world, but that's thankfully not the default setting. ;)

Requires use of the console, so you need to have "-console" in your command line for Valheim.