Cant find MMS Message in settings?

I have and iPhone 5S, while trying to send a picture via text I discovered that I could not do it. A message saying that MMS is not enabled came up. I tried to follow the instructions online to enable but I don't have the entry that is being described to change it. Does anybody know why I don't have and how a iPhone like mine can enable MMS Messaging. I have also been through the process of setting proper APN settings when I could not receive MMS. Thanks