There are a couple of ways to change a user password including root for the mysql databases.
one is using mysqladmin(which i’m not that fluent with)
the other is directly go into mysql and change the password.
$mysql -u root - p
Now enter password (your old password for root)
mysql > use mysql;
mysql> update user set password=PASSWORD("new_password") where User='root';
mysql> flush privileges;
mysql> quit;
You can login again to check whether the password change took effect