How to update ValhallaMMO
Certain updates make changes to the default configuration of ValhallaMMO, this can include new/changed recipes, balance changes, or bugs to do with skill progression caused by wrong configuration.

Updating to a new version of ValhallaMMO doesn't fix these issues, as configs are not (and should not) be patched for such changes.

When updating to a new version of ValhallaMMO some further manual changes are sometimes needed, explained here.
Before doing anything with these configs you should make sure your server is turned off

If you haven't made any changes to the configs yourself and are content with the default configuration, it is safe to delete the entire ValhallaMMO folder. Data will not be lost since the data is not stored in this folder.

Recipes
If an update states recipes have been changed, most people can just delete the current recipes folder and let the plugin generate a new one on server startup.
Some people, however, decide to make their own recipes and changes. That's great! But if you want the new or changed recipes to be added to your server you should first backup or rename your current recipe files (if you don't care for the changes you can skip this section). Remember the names of these files because you'll need them later.
Once all these recipe files have been renamed or backed up, delete the previous recipe files (if you've renamed them you obviously won't need to do this).
When your server is running again, run the command /valhalla import false <file_name>.yml for each recipe file you have backed up. This command will load in all recipes saved in that file and keep existing recipes on the server untouched. If you replace false by true it'll instead overwrite existing server recipes with the recipes you imported, but you typically won't be using this one.

Configuration
Sometimes bugs are caused by a wrong default configuration, unfortunately the steps to fix this aren't as nice.
Of course, if you've made your own configured skill trees and stuff, you can ignore this.
Otherwise, delete all the progression_<skill>.yml files and start your server.
Players who have already been affected by the outdated configs will not be fixed afterwards, this needs to be done through a manual stat change or a soft reset. For a soft reset, the command /valhalla reset false <player> may be used. If true is used instead, the player will be entirely reset and start from 0.
A soft reset resets the player but restores their EXP so no progress is lost, their stats will be corrected and they can re-invest their skill points.
Alternatively you can manually correct these stats using /valhalla reward command, but this is a bit harder