Step 1: Login to admin area
Step 2: Go to Extensions and then Extension Manager.
Step 3: Open the Manage tab.
Step 4: Select Template from the Select Type drop-down menu.
Step 5: Search for the chosen template in the filtered results
Step 6: Click on the check box besides it.
Step 7: Find the Uninstall icon in the upper right
Step 8: Click on it to completely remove the chosen template.