Can/should I download iOS 7 for my iPhone 4?

Amy

IOS came out recently and I've seen the new icons, when I go to download it says I need 2.9GB of space and I only have 8.

Now I have 57 photos, 2 and a half pages of Apps and 43 songs and still not enough space.

John

Use iCloud and backup your apps. Delete a few, take a screenshot of what you already had, then download them again.

What is Difference between iOS 7 Download service and iOS 7 Beta download? While downloading the latest iOS 7 for iPhone 4, I have seen many pages around the web that are stating iOS 7 download as a separate service than iOS 7 beta download. So my question is, what is the real difference between ios 7 download and ios 7 beta download? both are same software update or different?
Should I download the iOS 7? I really want to try it out, but I don't want to restore my phone and lose all my messages, pictures, apps and everything I have on my phone now. Is there a way I can download it without having to lose all of that? And I'm not really familiar with iCloud since I've never used it. I have the iPhone 5 if that helps any.
Should I download IOS 9? IPhone 6? The only reason I want it is for the saving battery life cause my phone dies quick and can you guys say positive and negative things about it?
Should I download iOS 8.1 on my iPhone 5S? I've read a few reviews, and some of them say that their phone is slower now that they've downloaded iOS 8.1. Has anyone else experienced this? Apart from speed, what are the other positive and negative points of downloading it? I'm probably going to wait a couple of weeks anyway, so there's time for people to find all the bugs, but I just wanted an idea of what it's like.