If I update my iPhone software will it take up memory?

Basically I have a 16GB iPhone 4s. If i only 3GB of memory left. I don't wan't to remove any of my current content. So basically, if i upgrade my iOS will it take up any of this remaining 3 Giga Byte?

Nope,
Because it will delete the previous software and replace it with a new one. You could be looking at 100mb less memory than before so it won't take up hardly any memory