There is no possibility to delete a supplier entirely if it already keeps some history logs in the system. But you can disable a supplier, so it won't be available and visible in Precoro.  

To disable a supplier, please follow these steps:

        1. Please go to the Supplier Management → tab and click on Manage Suppliers;

        2. Click on Show filters and find the supplier that you want to disable;

        3. Then in the Action column, click on the edit button;

       4. Move switcher in the right side of the 'Edit Supplier' row to disable the enabled supplier or vice versa (a switcher should be grey and show "OFF") Update.

Now your supplier is disabled. 

You can always enable it again, just check this article.