There are many cases when you forget magento admin password .
For security reasons magento stores password inform of MD5 format in database , so you cant get password directly through phpmyadmin interface.
You can reset password using 2 methods :-
1) First find under which user you want to change password using below query:-
"SELECT * FROM `admin_user`;"
Now, to reset password run below query,
UPDATE `admin_user` SET `password`= MD5("newpassword") WHERE `username`='admin';
2) Go to phpmyadmin.Browse admin_user table . Edit specific record you want to update . While you change password in `password` field, select MD5 from dropdown under Function section & enter your password , it will store your password in MD5 format.
See below Screenshot for better idea :-
You are Done !!
Now try to login with new password !!