Step 1: Click on Activity in the Admin Left Panel. From the drop down, select Captures.
Step 2: Click on the user you wish to delete the screenshot of.
Step 3: Select the screenshots and click on the delete icon to delete that particular screenshot.
Step 4: If you wish to select all screenshots at once, navigate to the top right corner of the screen and check the box next to Select All.
Step 5: Click the Delete Screenshot button to delete all screenshots.