To manually delete and re-download an issue, tap the downward pointing arrow icon in the extended magazine controls. 

When the downloads dialog pane opens, tap the “x” icon next to the issue you wish to delete, a confirmation dialog will open, tap “Yes” to complete the deletion, or “Cancel” to back out if you chose the wrong issue inadvertently.

Once the file is deleted, in the main library view, you will see the selection button change from “View” to “Download.” Tap “Download” to begin the download process again.