Does updating to iOS 7 delete everything on my iPhone?

I have an iPhone 4S, 16GB, and not jailbroken. I wonder if upgrading to iOS 7 will delete everything (apps, pictures, videos, and messages) on my phone.

No it will not!

No it won't, your data will be safe, although you could back up important pics and stuff on iCloud if something happens

No, but to be on the safe side you can backup you data

No it will not.