iTunes not offering iOS 5
Hi:
I have decided to upgrade my iPhone 3GS to iOS 5. With my iPhone connected to iTunes, when I click "Check for Update" I get a message that says, "This version of the iPhone software (4.2.1) is the current version." How do I get it to upgrade me to iOS 5?
Thanks
Mac mini (Late 2009), Mac OS X (10.6.8)