Can i replace the iphone 4 camera with the 4s camera?

Get it removed & installed
is it possible?

Only 3rd party companies would do that for you, so I would really not suggest it. I have heard of websites that take the back off and do a bunch of minor tweaks, but that is risky in so many ways. Just wait for the iPhone 5S or 5C. 5C is supposed to be cheap and durable but have a full 8 mp camera. Hope this helps!