Cancelling or declining a file transfer
If you've started transferring a file to a contact, you can cancel the transfer at any time, as long as the person to whom it was sent has not yet completed the download. Just click the Cancel link that's below the file in your chat window.
If you close your chat window during a transfer, you'll be warned that your transfer will be aborted if you continue. Click OK to close your chat window and cancel the transfer.
If you don't want to receive a file that's being offered to you, simply click the Decline link in your chat window. The file won't be downloaded to your hard drive, and the sender will be notified that you have declined the transfer. If it's an image that's being transferred, the thumbnail in your chat window will be removed.