How to restore my old OS on my iPhone?

I backed up my phone the other day and without asking me, the phone installed the new OS. It's the 4s It also deleted all of my apps that I have installed. It will not allow me to check the weather nor log my resents on my call list. I'd like to just revert back to the way it was.

I know, I should have gotten a better phone than the iPhone but I have what I have for now. I just want to go back to when it worked better until I can get something better.

If I can't restore the original OS, how do I at least restore all of my apps?

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Again, Hi2mic, How do I restore the apps which should be backed up?
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Unfortunately, you can't go back once the new version is installed.