I have iphone 3gs version 6.0.1 and I don't know how to enable the retina display?

I have iphone 3gs version 6.0.1 and I don't know how to enable the retina display?

My friend got his iphone 3gs 6.0 with retina display but we really don't know how to enable it in my iPhone

I'm sorry but the Retina display is only available from iPhone 4 onwards. And since it is a hardware if the phone has it, there's no need to enable it.

Here's the Specifications of an iPhone 3GS:
http://support.apple.com/...cale=en_US

As you will find, there's no Retina Display.

The 3GS doesn't have a Retina display, only the iPhone 4 and up have it. Sorry.

Retina Display is not something you enable. That was a hardware improvement from the iPhone 4 on up where Apple increased the screen resolution so that the PPI (pixels per inch) crossed the 300 mark as our eyes are able to discern up to that point, hence the name Retina Display.

The iPhone 2G to 3GS do not have Retina Display nor will they ever have that, so how your friend apparently got that is up in the air, either that or someone is mistaken.