If you're not used to asp.net, the sample project may be confusing as to how to alter the credentials supplied...they're technically in the aspnetdb.mdf..but that is not meant to be altered directly.
To edit credentials, do the following:
1) In visual studio, select the asp project
2) go to website, asp.net configuration
3) click 'security' and then go to 'create or manage roles'...setup your users and roles in there, or use the security setup wizard thats available on that page
That should get ya up and running with your own username/pw!