How to update to latest itunes on pc?

Okay so I just got the iphone 5 and i previously had the iphone 4 and i plugged my 5 into my computer and it did not connect for some reason. Itunes didn't pop up and it also didn't charge my phone.So, correct me if i'm wrong, but I guessed that it was because i dint like to update my itunes so i have an old version. And I know that when you click on itunes it asks you if you wanna update but i'm the stupid person that pressed never ask me again… So yea. ANyone have any idea how to do this?
Please and Thank you!

Go and download the latest itunes from apple site. Remove existing one from the pc Or try to install the new one without removing the old one.installation process might automatically remove the old one