Guild Wars 2

You can.
Simply drag empty bags into your other bags and you can put a new one in its slot.

Or you can just drag a bigger bag onto a smaller bag that you’re using. The items will stay the same, the smaller bag will appear where the bigger one was in your inventory and you’ll have you’re extra slots.

My suggestion is to ask for help ingame to figure out how something works rather than coming to the forums to suggest they change something that doesn’t actually exist in the first place.