Navigate to the Test Coverage primary tab, and then to the Builds secondary tab. In the details window of the specific build, click on the Test Sessions tab to show the list of test sessions for that build. For the specific test session, click on the menu icon and choose Delete.
Bugs created from a test session will not be deleted when a test session is deleted.
Users will need view, edit, and delete permissions in the test coverage module to delete a test session. Depending on the settings of a users project permissions, users may be able to view all project builds or just a subset of them. Project owners manage the permissions for project members.