Parallels is offering a free of charge upgrade to Parallels Desktop 8 for Mac for all customers who purchased a qualifying upgrade version, full version, student license or OEM version of Parallels Desktop 7 for Mac between July 25, 2012 and October 30, 2012 from an authorized reseller, such as Small Dog Electronics. Qualifying customers can claim an activation key for Parallels Desktop 8 for Mac until November 15, 2012.
See this link for more information and to request your upgrade: Parallels Desktop for Mac Tech Guarantee 2012