Hello and thank you for choosing JUSTANSWER.com
So, when you try to download...what happens?
Itunes should be downloaded from http://www.apple.com/itunes/
YOu need to run the system checlk to make sure Itunes 12 will run on your machine....but most likely it will be just fine.
But again, what happens when you try to download?
Also, what browser are you using to go online?