As there are frequent requests from users, who lost the password of the host account (and you cannot request the host password by email), the following solution will help for all DNN 3 and 4 installation. Please note, that your need direct access to the database to suceed with the issue:

• if "register" is not displayed for the portal, go to table "Portals"  in your database and enter value "2" into column "UserRegistration".
• create a new user account by registration (this time, please remember the password you enter!)
• go to database, enter table "ASPNet_Membership"
• 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 th first entry in this table) 
• login as user "host" using the new password and delete the reshly created other user.
• if changed, revert UserRegistration mode in Site Settings
• Keep remembering your password ;)