I want to update my iPhone 5S to iOS 9.1 but I'm scared that my apps won't work?

I have 2 free music apps that have like a million of my favorite songs and i don't know what I'd do without them. If this update screws things up I swear… I'm scared that if I do this update, my apps will crash and it will just ruin my phone in general. And I think I need to do this update. For the free music apps, there have been no updates in the App Store specifically for iOS 9. Just in case I always do back ups of my phone onto my Mac laptop (via iTunes). However if I update my phone & something's not going to be working, there's no going back. This is really important i don't know what to do

Believe me, If you update, Nothing at All will happen