CHEAP Return Train Ticket ?

I have a return train ticket from Edinburgh to London return for the last weekend of September. Unfortunately I am no longer free to use them. Dept 28 September 2012 at 15:30 (price 10.90) Return 30 September 2012 at 17:00 FIRST CLASS (price 39.20) Both are Edinburgh Waverley and London Kings Cross and a Young Persons is required. Please get in touch ASAP if you are interested and we can arrange an exchange. Georgina :)