You should read through the terms of the agreement, and then click "Agree".You have to agree to the terms in order to download the software.
You'll have to review and accept the i Tunes Software License Agreement before the new version will launch.
Note: Apple's updater is likely to suggest additional software that you can download (such as the Safari browser); none of this is necessary.
You can download it if you like, but you don't need it to update i Tunes.
Let this run; do not disconnect your i Phone while it is doing so.
When the update process is complete, i Tunes may not give you any notification.
Sometimes, i Tunes just automatically disconnects your i Phone from the software and then connects it again.