Ios 8.4 imessage issue, how do i fix it?

I updated my iphone 5s yesterday to ios 8.4 and ever since then, i can't open all converstations in imessage. And some of them that do don't show every message. It freezes and can't go back to the previous screen. Anyone know how to fix this?

Try turning your phone of then on. If that doesn;t work, double click the home button once youve unlocked your iphone.It'll show all the apps that you ahve used.Swipe it up. Then try.Either that or go to an apple store.