If you have recently bought the latest version of the software MEP 2013) then either :-
- contact sales at Magix if you purchased direct from them
- otherwise try contacting the supplier you purchased the software from.
If you have purchased an older version from a retailer 'on special offer' as several posters on this forum appear to have done in the US , then your options may be restricted.
Interesting that the only question you have asked on this forum is how to get a refund. John is absolutely right, if you bought it direct from Magix, and are within 30 days of purchase, contact Magix sales. If you bought it as a boxed version from a retailer, good luck.
Why have you never posted a question about any issues or problems you were having with the product?