To remove a work from the sale on the site, you have two possibilities. The first is to remove the work.
To do this, click on the work's file and then on "Delete".
The second possibility consists in indicating on the site that the work is sold out (the work will then bear the sticker "Sold Out" instead of the price and users will no longer be able to buy it).
To do this, click on "Mark artwork as sold out" or change the number of copies available to '0'.