Military/24 hour time stuck on unlock screen

Can someone please help me?

When I first got my phone I let my friend change the settings because he had an iphone. However he accidentally changed the time to the 24 hour clock. We changed it back, and it worked--sort of. The time displayed when I use the phone is the correct standard time. However the "unlock" screen is still displays it in Military time and we could not figure out how to change it back.

I'm hoping someone knows how to change it back??