You can unschedule your listings either singly or in bulk. To unschedule a single listing, click the listing title then scroll to the bottom of the page and click the "Undo Launch" button.
To bulk unschedule your auctions, first click the "Pending" link under Display Options in the lefthand navigation bar. On the next page, select the listings you want to unschedule and click the "Cancel" button at the top of the list.
If you would like to reschedule the listings, select the items again by clicking the check-boxes next to them, and then click the "Resubmit" button. On the next page, you will have the option to launch immediately or reschedule the auctions to launch at a later time.