http://www.allearsnet.com/pl/ticket.htm#6
TICKET MEDIA CONVERSION - By converting your tickets to the current magnetic strip ticket media, you pay nothing and allow for the ease of use with the new magnetic strip reading turnstiles. Your magnetic strip passes can also be used in the FastPass machines. This allows everyone with any days left on their old WDW tickets to use them.
You can convert these passes at any major park ticket booth or Guest Relations window at no charge.
I have some old passes with leftover days that say they are only valid for entry to the Magic Kingdom and Epcot. Are those still good?
Yes. Have them converted to the magnetic strip ticket and you can still use them. Oh by the way, once you do the conversion your days can be used at any of the four major parks now.
EXCHANGING OLD CHILDREN'S TICKETS
Many people find themselves in the situation of going to WDW with their young children and having unused days left on their tickets when they return home. These tickets are put away, often for many years, until another trip to Disney is planned. But what can you do with these tickets since your then child is now a teenager or even an adult and obviously can't use a child's ticket now?
What you have left will depend on how this transaction is handled. If you have a brand new, completely unused child's ticket that you bought years ago you will only be able to apply a dollar value equal to the price you paid for that ticket towards any new adult ticket that exceeds the price of the old one. This is your only option with an unused child ticket.
But if you have a partially used ticket, you may take that ticket along with your child who is now a teenager or older to a Guest Relations location at the major parks or DTD. If the Guest Relations CM is satisfied that the dates of the original ticket and the current age of your child make sense, you will have the leftover child's admissions exchanged for the identical adult admissions at no further charge to you. The "child" must be with you or you will be unable to do this.
Making sense of the dates means that if you bought and used the child ticket in 1994, then your child in 2004 must now fall in the 13-19 year old range. If you bought and used it in 1984, then the "child" must now be in the 23-29 year old range, etcetera etcetera. If they are not, then Disney reserves the right to offer you nothing more than the dollar value of the unused admissions towards a new adult ticket.