Please note that you will have to update the vendor/supplier number both in your 'My Suppliers and Account Payable hub.
In 'My Suppliers'
Navigate to [Suppliers] - [My Suppliers] and search for the Supplier you would like to amend. Note: you cannot search by Supplier Number.
Select the [Edit] icon alongside the Supplier's name as seen below:
Remove the old number and add the new number, followed by [Update].
In your 'Accounts Payable Hub'
Navigate through Settings → Accounts Payable, then click on the 'view' icon.
Go to 'Suppliers' Tab.
Search for the supplier that you want to change the vendor number.
Click on the vendor number and remove the current one, then replace with the new one. Once done, press enter to save.
Congratulations! You have amended the Supplier Number.