If you do a lot of texting, your Message app is probably clogged with old messages. Before iOS 8 you had to manually delete conversations or individual messages. Now you can set the app to automatically delete all messages older than 30 days or one year. The default setting lets you keep your messages forever, which could be handy if everything you write is a gem of unparalleled wisdom. Everyone else, read on:
Go to Settings>Messages and tap Keep Messages to open.
Select 30 days or 1 year and your iDevice will start automatically deleting messages once they are older than your chosen time period.