Log in to your control panel at:
http://cp.mydomain.tld  <-- replace mydomain.tld with your domain name

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From the Main Menu, Click the 'My Domains' icon
 

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This will show you a list of all the domains in your control.
Click on the domain name where SmarterStats is installed.

 

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From the Edit Domain screen, Click the 'SmarterStats Web Statistics' icon:
 

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The 'SmarterStats Web Statistics' page will show you your *SiteID and *Login. 
**You will need BOTH of these in addition to the password to access the Stats pages.

SmarterStats has no option to 'recover' a lost password. You will have to change it.
Note the 'Change Password' button in the blue navbar