Retailers need the flexibility to make changes specifically to the mode of delivery on customer order sales lines at any time prior to the fulfillment of the line.
Change Mode of Delivery can be added to a point of sale (POS) screen layout. It will be applicable only to lines that were previously configured using the “ship all” or “ship selected” methods for creating orders in POS. After the original mode of delivery is set for a transaction line, a user might want to modify the mode of delivery for one or more eligible lines without having to go through the entire “ship all” or “ship selected” flows. The mode of delivery operation will provide this convenience. It can be used during the initial order creation processing of the POS customer order, or during the editing of a customer order. It is not applicable to lines that are not configured as shipping lines, and the operation will not work for lines that are already released to fulfillment or invoiced.
If you want to change a line designated for pickup or carryout to ship, you must use the Ship all or Ship selected operations. Conversely, if you want to change a line designated as a shipment to a pickup or carryout, you must use the Pickup all, Pickup selected, Carryout all, or Carryout selected operations.
What this means is that, you can not change the mode of delivery from Shipping to Pick up.
As you can see here, the change mode of delivery button can do this job.
In previous versions of Retail, you had to go through the full Ship all or Ship selected configuration flows if you wanted to change the mode of delivery on an existing line that was configured for shipment.
Hope this helps!