If you lost the password of the host “superuser” account (and you cannot request the host password by email), the following solution will help for all DNN 3 and 4 installations. Please note, that you need direct access to the database:

1. Go to Register a new user on your DotNetNuke Site. If “Register” is not displayed for the portal, go to table “Portals” in your database and enter value “2” into column “UserRegistration”.
2. Create a new user account by registration (please remember the password you enter!)
3. Go to database, and find and enter the table “ASPNet_Membership”
4. Go to new user account (usually the last one) and copy the encrypted values of columns “Password” and “PasswordSalt” into the same columns of user account “host” (usually the first entry in this table)
5. Login as user “host” using the new password and delete the newly created other user.
6. Complete!

source: Reset DNN host user password