Hi,
Try to maximise the window of the "Runtime Security" window.
You should then see an icon for adding User/Group. This icon is not shown in your screen shot, but should appear once you maximise the window.
You should then be able to delete the user "SPRV".
Now to delete the User "SUPR", you do a Right Mouse click on the left window pane where SUPR is shown under the folder "Users & Groups" then "Users".
If you are still struggling, post back & I will provide screen shots later...
Ian