When you update your iphone, do you get that data back?

Okay, so I'm a bit technologically dumb… The new ios7 for iPhone came out and I want it. I have an iPhone 4. I went to download it and it said I needed 2.9gb to download. So I deleted some apps and got up to 2.9GB so I could get it. What I'm nervous about is that I only have a 5GB plan and I can't delete anything else since I use it all on a regular basis. My question is will I get the 2.9GB back after I download ios7? It's just a phone update, I don't really see why I wouldn't but this is my first iphone and I really don't know much about iPhone except the basic ways to use one.
Also, is the ios7 even worth it if I'm losing almost half my data for it?

How could you get your data back if iOS 7 takes up 2.9 gb? No you won't get the data back.iOS 7 takes up 2.9 gb that's way you can't get it back