Thanks for all your replies. I bought UT 5 day (one park per day) instead of hopper for 2 adults for $643.90 total. Disney is showing 2 adult (park hopper) tickets for total of $807.28 including taxes. I'm thinking it will cost me $163.38 to change. Am I correct? I still don't quite understand using tickets before changing or go to guest services first. I hope they don't give me a hard time because I don't deal with confrontation well. I'm a wimp!
Disney price for TWO 5-day base tickets is $670.96 (including tax.)
Disney price for TWO 5-day HOPPER tickets is $807.28 (including tax.)
After using your tickets to enter a theme park at least one time BEFORE upgrading,
you will owe the difference price from the above numbers, or
$136.32 to upgrade both tickets (including tax.)
It does not matter in this situation how much you paid for your UT tickets.
Disney has no way of knowing what you paid for your UT tickets.
Disney only knows how much UT paid Disney for the tickets.
And, if you don't USE your UT tickets at least one time to enter a theme park
before you upgrade, Disney may attempt
to charge you the difference from the wholesale cost.
NOT GOOD.
Because if that happens, you'd be paying more for your tickets than if you had bought them from Disney originally.
Ask the CM at the ticket booth or Guest Relations how much the cost will be to upgrade when you first show her/him your tickets.
If the cost is more than $136.32, just thank the CM, say that you've changed your mind, and take your tickets back. No confrontation needed.
Then, go to another ticket booth or Guest Relations at some point before you want to park-hop.