It's not an early upgrade. Verizon has two upgrade programs, New Every 2 and Annual Upgrade. We all seem to know what NE2 is, however the Annual Upgrade is just that, you can upgrade once a year and it resets your NE2 so you will not get the extra discount. Annual Upgrades give you the discount price that new users typically get, and you resign a contract for another 2 years. So you are extending your contract to two years again, and wiping your NE2, and getting the advertised discount price (you are also required to have a plan that is 49.99 or more). As far as I know, this can only be done through verizon themselves (e.g. best buy can't do anything but NE2). You can do it in store, on the phone or online. Click upgrade phone, and it will list your NE2 status, but if you go down there will be a help faq that talks about the annual upgrade. If you are eligible, the discount will appear when you click the phone to upgrade, unless you have NE2 available, and I believe that will take precedence (since you get the phone cheaper with it).
An early upgrade is verizon themselves waiving restrictions (such as a month to go on NE2 or Annual Upgrade) and allowing you to upgrade anyway.
Hope that helps.