The only way to expand your inventory and warehouse storage in Archeage Unchained is to get expansion scrolls. A single scroll will expand your inventory or your warehouse storage by 10 slots. You can at most use 10 expansion scrolls for your inventory and another ten for your warehouse storage.
Getting Expansion Scrolls
As far as I know, there are only two ways to get expansions scrolls in Archmage Unchained, by buying them from the diligence shop or the auction house.
Buying Expansion Scroll by Using Diligence Coins
In the diligence shop, under the luxury tab, you can buy an expansion scroll for 30 diligence coins. Have your diligence coins in your inventory, press the bag icon and then press purchase. You should now get your expansion scroll sent to you in your marketplace mail (separate from your regular mail).
Buying Expansion Scroll on the Auction House
You can also buy expansion scrolls from the auction house. The price will obviously vary from day to day, but one would expect the price to stabilize at some point in the future in connection with other items you can buy with diligence coins. When this is written the price for an expansion scroll is about 75 gold (Nov, 2019).
Using an Expansion scroll.
To use an expansion scroll to expand your inventory or warehouse space you first need to have it in your inventory. To expand your inventory you then need to open your inventory and press the + symbol. You then just need to confirm and your bag is now 10 slots bigger.
To expand your warehouse space you do pretty much the same, except now you need to open your warehouse and press the + symbol in your warehouse storage.
Other Ways to Get More Storage Space
If you have a house you have a few options to get more storage space. One of them is the Otherworld Storage Chest, which gives you a 100 slot storage once you place it in your house. This piece of furniture can be bought for 180 diligence coins or 1675 credits.
You can also craft a variety of chest, some are specific to a type of item (e.g gliders) while others are more general. As an example, the Spacious Storage Chest has 50 general storage slots and the 50-slot rider’s trunk can store fifty items that are related to mounts.
So that’s about all there is to expansion scrolls in Archeage Unchained. I have a few other guides you might be interested in and if you find them useful then please share them with your friends and allies in Archeage.