This is currently a known issue and there is no current ETA on when this will be resolved. However, the following instructions will walk you through deleting the game folder once you have uninstalled Aion Classic/Aion through the NC Launcher.
- Go to the Aion Classic/Aion folder.
- Delete all the contents of the specified folder.
Note: This will free up space once the content has been deleted.
If you have any further issues, please contact support HERE