If you don’t count the iPhone 4S (and most analysts don’t), it’s been more than two years since the company offered a major upgrade to its most important product — the one that generates more than half of Apple’s revenues and is almost single-handedly responsible for the stock’s 600% growth over the past five and a half years.

Much has changed since the iPhone 4 was unveiled in June 2010. Steve Jobs is dead. Google’s (GOOG) Android dominates the smartphone market. The hottest-selling mobile phone today is made by Samsung — not Apple — despite a jury verdict that dinged the South Korean manufacturer $1 billion for stealing Apple’s patents.

So what can we expect at Wednesday’s press conference? There could be a surprise or two, but in terms of the main event — the launch of a new iPhone — the tech press seems to think it knows what’s coming. The key changes:

• A larger screen display (4-inches vs. 3.5 inches)
• Taller and slightly thinner format
• More durable unibody casing
• Smaller dock connector (Apple will sell an adaptor to connect to old peripherals)
• Faster processor
• More memory
• Support for the fastest 4G LTE wireless networks
• All the known features of iOS 6 — Apple’s 3D maps, improved Siri voice technology (with sports scores, movie times, restaurant reviews, and so on), Facebook integration, Apple’s new Passbook purchasing feature, etc. — and maybe a few new ones
• Prices starting at $199, with two-year contract

We’re stuck in Brooklyn for this event, but we’ll be monitoring the tweets and live blogs and will try to offer some useful analysis as the news unfolds.

UPDATE: No extra memory. Otherwise, the event went pretty much as expected.