Hi,
If you have additional Global Admins in your organization, they can reset the password for you. If your account is the only global admin account, but have additional email address mentioned during account creation, refer this
link.
If you don't have any of the above, open a support ticket by using the resources below:
http://support.microsoft.com/gp/Cloud-and-Online-Services#tab0
Regards, Chandra.