As with last time, some people are reporting problems while trying to download the 4.0.1 iOS update for their iPhones, where their network connection is interrupted and the download cancels. It’s also painfully slow when you’re in Australia or other third world (as far as internet connections go) countries. If you’re one of these people, you can grab the direct downloads here. They’re all direct links to the Apple servers.
Downloading direct is also a lot faster, especially if you’re using a Firefox add-on called “Down Them All!” which splits downloads into multiple chunks so that instead of being restricted to a single slow download, you can run ten slow downloads concurrently – effectively making your download run ten times as fast.
Once you have the file, connect your iPhone to iTunes 9.2 and perform a backup, then hold the Shift key (Windows) or Option key (Mac) while pressing the Upgrade button and select the firmware you downloaded to begin the upgrade process, or the Restore button if you want to install fresh.