Business profile
Your business identity, and why country and currency are fixed.
User guide
Your business identity, and why country and currency are fixed.
Your business is the account itself: one owner (the Administrator), one subscription, one country, one currency. Everything else — stores, staff, products, orders — lives inside it.
Who can do this: every staff member can open Business profile (from the sidebar's user menu) and read the identity facts. Editing happens on Business settings and is the Administrator's alone.

Your currency is derived from your country, once, at signup — and every store you ever create uses it. A store's currency field is shown but permanently locked; whatever a store is asked to be, it trades in the business's currency.