I just found out how to do it:
Swipe up for apps and choose email.
From your email inbox, click on menu (those 3 horizontal bars)
Then click on settings
Click on your email account (if you have more than one, the setting you choose for the default will be on all).
Scroll down and click on "server settings"
(At this point my keyboard opened up and I had to close it before I saw all the options on the server settings page).
Half way down there's an option for "Delete email from server" and you can toggle between "always and "never".
I just adjusted mine (all of a sudden deleting emails from my server).
Hope this helps.