Iphone 4 5.1.1. To Update version iOS 6.1

Connect to iTunes on the computer you usually Sync with and “ Check for Updates “...

See the Using iTunes Section Here...

How to update your iPhone, iPad, or iPod touch

Note:

The Current iOS for the iPhone 4 is iOS 6.1.3

Have you followed the directions as outlined in your previous post?

What issues are you having?

Error messages?

http://support.apple.com/kb/HT4972