Once you buy a Cisco equipment, through your sales rep, there should be a contract number, thats used as a reference for your purchase. Using that contract number, you can signup for a CCO login.
Visit http://tools.cisco.com/RPF/register/register.do
Once you have a CCO login, you can login to the Cisco Software Center, for downloading new IOS versions for your product.
A link to software center - http://www.cisco.com/public/sw-center/
Hope that helps!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus