With the new update, and the new save file format (which should help with a lot of the disk usage issues from having very large save files), your old save games are no longer compatible with future versions of Archmage Rises starting with version 0.0.13. The newer save file format is leaner which will not only help cut down significantly with the amount of disk space older save files consumed, but also boosts performance in load / save times.
So what are you do to with the old save files? Well, the game doesn't automatically remove them from your hard drive, so you are welcome to go ahead and delete your old saves in order to save some space.
Here's where you can find your old incompatible save games (and worlds) to trash if you want to reclaim some of that disk space:
NOTE: If you've already updated to patch 0.0.13, in these folders you'll find both files directly inside the GameSaves / Worlds folders as well as folders inside these folders. Those new folders contain your new saves/worlds so you'll want to retain those, but you can delete any of the files that are directly inside the GameSaves / Worlds folders.
WINDOWS:
C:\users\yourusername\AppData\LocalLow\Defiance Game Studio\ArchmageRises\GameSaves
C:\users\yourusername\AppData\LocalLow\Defiance Game Studio\ArchmageRises\Worlds
MAC:
/Users/[username]/Library/Application Support/Defiance Game Studio/ArchmageRises/GameSaves
/Users/[username]/Library/Application Support/Defiance Game Studio/ArchmageRises/Worlds
LINUX / STEAM DECK:
/.local/share/Steam/steamapps/compdata/506480/pfx/drive_c/users/[username]/AppData/LocalLow/Defiance Game Studio/ArchmageRises/GameSaves
/.local/share/Steam/steamapps/compdata/506480/pfx/drive_c/users/[username]/AppData/LocalLow/Defiance Game Studio/ArchmageRises/Worlds
That's it! That should get rid of your old incompatible saves and give you some of your disk space back!
Phil