Premium edition upgrade includes Dark Side Cookies bonus DLC that features:

• Clot of Darkness amulet providing bonus to money and experience 
• Two additional locations 
• Over a dozen additional quests and a new unit

Please note: Owners of Premium edition have this DLC already.

Please note: You'll need to start a new game to create the game world with new content. If you continue a save started in regular edition, premium content won't be available.