Identifying the template to delete, clicking the dropdown arrow at the right end of the row, and selecting Delete. Or:
Selecting the checkbox of the test template to delete and clicking the Delete (trash can) icon.
Click Ok to delete the test template.
Use caution when deleting test templates. Deleting a test template also deletes all test cases based on the template. Test run results in already-completed test runs based on the edited test templates are unaffected, but rerunning the test run will not include the deleted test cases, producing results that differ from previous runs.
The Force.com multitenant architecture limits cascading deletes to 100,000 combined object records. Before deleting a test template or test case you suspect might have more than 100,000 associated records, first delete the associated test runs to avoid causing a situation that requires the assistance of Salesforce support. Refer to the Delete Operation Too Large Salesforce knowledge article for details.