There are two ways to delete a release in Wizeline. First, from the Roadmap view, click to expand the release in question, and click to view the release overview. Click the trash can button at the bottom of the release detail drawer, and confirm your action in the dialog box that appears. (Click to see this in action)
Alternatively, you can delete a release while in Plan mode. Visit Features, and click Plan. Hover your mouse over the release in question, and click the trash can icon that appears. (Click to see this in action)
Once your release disappears from the roadmap or the list of releases in Plan mode, it will no longer appear for any other user in Wizeline.