itunes will not update, no matter how many times i click the button to update it

I cannot connect my iPhone 5s (iOS 8.3) to my iTunes account because my iTunes needs to be updated, but every time I click the button to download the update when the message pops up, nothing happens. I have also gone into the help tab on iTunes and then selected 'check for updates' which then gives me the option to update, but still nothing happens. I'm getting so frustrated as at the moment I have no music on my phone at all, and I cannot back my phone up to my laptop. Also, my laptop is up to date if that helps. Any help is much appreciated!