Build files and artifacts can be deleted only if the build has not been released for testing. Once a build is released for testing, build files and artifacts can not be deleted.
Navigate to the Test Coverage primary tab, and then to the Builds secondary tab. In the details window for the specific build, click on the build artifact icon on the right side vertical menu. To delete a build artifact, click on the the vertical menu for the specific file. From the drop down, choose Delete and confirm your choice. If you do not have the option to the delete, then the build has already been released for testing or you do not have permission to delete artifacts.
Users will need view and edit permissions in the test coverage module to delete build artifacts. 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.