Issue with bulk importing into commerce (updating existing products)

Issue with bulk importing into commerce (updating existing products)

Hello All, 

I'm struggling to bulk update my existing products within my shop. 

I have exported all the products and appended the image url (copied from another product within the file) and then important back into commerce. 

The file is accepted but flags that no new products will be uploaded due to their being duplicates (which is correct) but I don't see a message or notification to say that it will update the existing product fields. 

Am I the only one having this issue? I've followed the online manual but it just doesn't work for me. 

Any help would be greatly appreciated. 

Kind regards, Richard