You can update supplier and contact details from the supplier details page.

Update Supplier Details

On the supplier detail page, click Edit Supplier.

Update relevant client details in the Overview, Contacts and Customer Prices tabs on the edit details page:  Click Save to apply the changes.

Update Contact Details

Supplier Contact details can be updated 2 ways, 

1. Contact details can be edited bia the Edit Supplier page:

2. Contacts can also be edited directly from the supplier detail page. Click Edit on the contact you need to update.

Edit the relevant contact details and click Save to apply changes.