Can I just update iOS6 or do I have to upgrade to iOS7 on iPhone 4?

I'm getting an iPhone 4 (on Virgin Mobile) for Christmas. I'd love to be able to just get the iPhone5, but can't afford that much at the current time. This iPhone 4 comes with iOS6 preinstalled. Now, can I just update the iOS6 - or will I be forced to upgrade to iOS7? I've heard horror stories about phones slowly dramatically after the upgrade, to the point of no longer being functional. I can't afford to fix my phone if it breaks after the upgrade, so I would essentially be stuck with a $200 piece of garbage.

My brother and his girlfriend both have iPhone 4's (albeit on either US Cellular or Verizon) that they have upgraded and said they had no problems. However, I just want to make sure. My iPad 2 seemed to handle the upgrade just fine.

TL;DR - Will I be able to update iOS6 or will I be forced to upgrade my iPhone 4 to iOS7?

I have an iPhone 4 and I'm not upgrading to ios 7 because I've heard many horror stories about ios 7 including the whole phone shutting down and deleting all the contacts and internal memory. So my friend actually had to spend money getting it restored. And also how the entire phone will start to lag a lot. And the battery drains super fast. Of course ios 7 won't face any problems on iPad 2 because it is running on a different system than iPhone 4. IPhone 4 is running from a older system among all the other iPhone like 4s, 5 and 5s. I suggest if you really like ios 7 that much, buy an iPhone 4S instead.It'll be able to handle the upgrade to ios 7 better

Follow these instruction to save your mobile SHSH blobs, then you will be able to downgrade from IOS 7 to IOS 6

http://www.cydiawater.com/download-tinyumbrella-to-save-shsh-blobs-from-cydia/

You can update or downgrade what ever you can, in that case you have to download IPSW file & do it with 3rd party Apps: Find here