When ordering beer, you will be presented with all applicable packaging type options on the product details page. These options can include By the Bottle, By the Can, or By the Keg, and will appear in tabs to the right of the product image.
Locate the tabs and choose your desired packaging type.
If additional packaging options are available (i.e. 6-pack, 12-pack, etc.), they will appear in a list below the tabs.