Matthew Sub-accounts (or bank account in general) can only be archived, not deleted. Look for the menu option for that if you want to do that.
However, I would recommend just going to the Visibility settings under Profile > Settings and hiding the sub-accounts that you don't need right now. Later, if you ever need more sub-accounts, you can just make them visible again and give them appropriate names and icons for your needs. That way you don't have so many archived accounts, which also can make your tax statement simpler (depends on how you handle it of course).
