For a current listing click on Revise Your Item, top left of listing, and untick the auto relist option near the bottom, above submit. But that may depend on how you originally listed it.
If it does relist you can end it early via More Actions, far right of item on your selling page > End Item (on My eBay classic view).
For future listings on a PC/laptop you can cancel it during the listing process just above submit.
