You can suppress delivery methods for customers booking online to remove the option of COBO/Will Call where other options (e.g. e-tickets and postal delivery) are available. This can be done on a delivery method basis for all Web Ticket Types; in the Admin Interface, go to Pricing > Ticket Types and, under Web Availability, hit the Edit button, tick the Suppress if possible check box beneath the COBO column, then hit Save:
It's worth noting that you don't need to change the Always available option here; once Suppress if possible is selected, customers will only be offered COBO delivery if no other option is available to them. If you're offering e-tickets with no limit to their availability, make sure that the Print box is checked for all applicable Ticket Types and that there is a PDF template and Ticket Design against every Instance - then customers online will never be offered the option of COBO/Will Call delivery.
However, please be aware that this change is global: any Instances that are on sale that have a delivery method other than COBO/Will Call available will not offer COBO/Will Call as a delivery method.
As this option only refers to web availability, all delivery options will remain available in the Sales Interface, meaning COBO/Will Call remains an option for customers who aren't able to book online.