Can you unequip an inventory bag?

You can unequip bags simply by dragging and dropping them into one of your other bags or dragging another bag on top of it. However, you need to make sure the bag you are trying to unequip is empty, otherwise this will not work.

Just drag the bag icon to a free slot in your inventory. It worked for me.

Also, you can substitute one container with another. Drag & drop the new box on top of the bag you want to substitute, just like you could do when you equip a new piece of armor over an old one.