Open Settings from the Company section of the menu (Admins only). It has seven tabs: Company, Depots, Attendance rules, Pay settings, Public holidays, Invoices and Notifications, each with its own Save button.
The Company tab holds your name, phone, email, address, time zone, currency, units and logo. The logo appears on labels, invoices, the tracking page and the customer portal. The sales tax rate and "How customers pay you" are on the Invoices tab.