Navigate to the Library via the Page Navigation Menus on the left, and select Suppliers.
Now find and select the Supplier you wish to edit, once selected it will open up that Suppliers page with all the relevant details. Here you can edit/update any of the details relating to this Supplier such as Contact Details, Supplier Locations and Stocked Brands.
Once you've made all the relevant changes to the Supplier, select the SAVE CHANGES button in the bottom left hand corner of the screen, or select the CANCEL button if you wish to discard any changes made.