I can't download itunes

A few months ago my itunes wouldnt work and it told me to uninstall it and reinstall it and thats what i did but it still didn't work and i have now given up on it but my sister has just got me an iphone 4s and i need itunes to download apps on it and i can't because i don't have itunes and i have tried to install it again today but it says i need the 64-bit or something and i don't understand also i use firefox and have windows 7 if that helps please help i have tried everything from asking the itunes people and from downloading different things to see if there's anything left behind of my old itunes and nothing works please help!

You need to completely uninstall iTunes, then download the correct iTunes for your operating system (32 bit or 64 bit), and reinstall.

Instructions: http://www.computer-answers.ca/2012/computer-questions/windows-questions/q-itunes-is-not-working-in-windows/