To expand your vault, you need an item called "Vault Expansion Certificate".

 
1. Talk to «Wandering Merchant Zyro» and accept the quest.

• Coordinates.
• Noria (186,109)
• Devias (226,52)
• Elveland (55,199)

• Quest «Ancient Statue» to expand the Vault. - You can get Ancient Statue from Death Knight at LostTower 6/7.