How to delete Release/Cycle from a Project?

For the Release/Cycle that you want to delete, go inside the Project "edit" mode and click on the Archive button under the Action column against the release.

Once the Release or Cycle is archived, it cannot be edited or modified further.

Note: If a Release is archived, then all the Cycles under the Release are also archived.

The Action column now shows Unarchive and Delete buttons for archived Release/Cycle.

To delete the Release/Cycle, click on the Delete button. The Release/Cycle should be archived first to delete it.

To unarchive the Release/Cycle, click on the Unarchive button.