iPhone 3GS and 3G owners, and iPod Touch owners can start iTunes and click the update button. Many have noticed that at approximately 1 PM EST, the iOS 4 was ready for download. If it isn’t live for you yet, keep hammering that update button until it is.
It is important to note that you’ll need to have iTunes 9.2 installed in order for this to work. Since many people are complaining that iTunes is very slow, here are the direct update links. They are courtesy of TUAW.
This way you don’t need to wait for iTunes to tell you you’re ready for an update. YOU’RE TELLING IT.
and iPhone 4
To install these from the Mac, hit the update link while holding down the option button, so you can select the file you downloaded from your hard drive.
If it seems to be taking a long time, don’t worry this is normal.