Make sure to use your tickets thru a park turnstile first, before doing your upgrade. This is the only way you will get the June 3, 2012 price credit for your 10-day tickets. Otherwise if you don't use your tickets first, you will owe the price difference between your tickets and the new price of those tickets.
June 12, 2011 to June 2, 2012 10-day Base ticket = $291
June 3, 2012 10-day Base ticket = $318
Price Difference = $27+tax
Cheshire Figment writes in the ticket sticky "Everything About WDW Tickets" (at the top of this forum), Post #6, paragraphs 7&8.
http://www.disboards.com/showthread.php?t=1452684
If you purchased your MYW ticket at a price less than the current gate selling price for that ticket (such as from a discounter/broker or Advance Purchase) and you wish to do any upgrade, Disney will not penalize you for the discount provided the ticket has been used. We will make an "intermediate" ticket at the current gate price, charging the difference between your old ticket and the intermediate one to an internal voucher account. Then we will take the intermediate ticket, which is at the current gate price, and upgrade it with the additional days and/or options you want, and you will only be charged for the differences in the current gate price plus tax. Note if you had paid full current gate price for your old ticket the intermediate step is not done.
If you purchased your ticket at less than the current gate price, and your ticket has not been used, you will have to pay the difference between what Disney actually sold the ticket for and the current gate price of the ticket you are upgrading to. It is always best to use one day from the old pass prior to taking it for an upgrade; you will then have locked in the current gate price as the value of the old pass.
So use your ticket first, enter the park, go to guest services inside the park, and do your upgrade. You can do the upgrade later. This just gets it out of the way first thing.