Save a copy of your configuration settings to a local PC and perform a factory reset using the Reset button on the rear of the DNS-320. While the DNS-320 is powered-up, press and hold the Reset button for > 8 seconds. This procedure will erase all of your user settings, which can be uploaded via the configuration settings file and should not impact previously formatted HDDs or data.
Before you perform the factory reset, save the configuration settings file and try to upload back into the DNS-320 it to ensure the file was created properly and works.
As always, when performing a reset or upgrading firmware, you should maintain a separate physical backup of your critical data.
Try to upgrade the firmware before loading your configuration settings.