You may need to delete an issue after you uploaded it. 

You may not want the issue any more and just want to fully delete it from your account (THIS OPTION CANNOT BE REVERSED!!! You may want to DISABLE your issue instead for a less permanent result)

OR you may be within the 12 hour grace period and need to delete because of mistakes, errors, or conversion problems (you get your Upload back in this case)

To delete an issue for whatever reason, navigate to the "manage titles and issues screen" and click on the trash can to the right of your issue's mini-cover thumbnail.  Once clicked you will be taken to a warning/confirmation screen which will ask you "Do you still want to proceed with deleting this Issue?". Click YES to follow through with delete, click NO if you want to cancel the delete.

See screenshot below:  Delete the issue on the left and you will get your Upload back for re-use; Delete the issue on the right and you DO NOT get your Upload back for re-use

Issues - Delete Issues Screenshot