1. Open Retail > Stock Management (top-level Retail tab in the admin menu) and expand the location.
2. Click Edit Stock on the meal/portion row. The Stock Movement pop-up shows the meal and portion and the current Stock available.
3. Type of movement is Remove Stock; enter the Quantity to remove and choose a Reason of movement from your Stock Management Justifications (all fields are required).
4. Click Save movement. Sprwt logs the movement with the stock before, the reason and your user, subtracts the quantity from the location's stock and re-checks the meal's stock alert.

Adding stock is done from the Retail Menu / stock upload screens rather than here.