The first page you get in the "Delete a Crew" section will list all the crews you have entered for your club. You can click on the radio button of the crew you want to modify in the case shown below we are going to sink Cantabs M1 crew. Next click on the "Sink Crew" button.

Now you will see the crew as shown below and if this is teh correct crew then just press the button and the crew will sink... glug...glug.