Go to Setup >> Customers. 

  Search for the customer account, under Actions column and select Edit.

The "Customer Information" window will pop-up. 

Under the Setup tab, click on the link: "Advanced".

Go to the "E-commerce Settings" section and configure the "Allow changing custom product packs" .  The company user can see more information about this field by hovering over the "What's this?" link. After finishing, click on "Save".