Solve problem on itunes updater

How to solve problem with itunes updater.?
I have tried to install the latest version of iTunes in my iTune and iPhone iOS 5. When opens the iTune the small windows is not pop up and so I am searching for updated by ‘Search for updates’ in the Help. Then a pop up windows is asking for to download the new version of itunes that is Version 10.5. When I am clicking the download, nothing is happening. If anybody knows why this is happening, please advice me to solve this issue.
