Go to My Tests and clicktap the test.
Then click the pause button on the right side.
Then tap the button on the right side.
Once a test is stopped (per the instructions above), the pause button is replaced by a delete button.
Click the delete button to delete the test.
Tap the button to delete the test.
Go to My Tests and look in the top left of your screen for a + New Test button.
That button will bring up a screen showing you any photos you've uploaded. Select the last box which says "Delete Photo(s)."