How to change the Mysql users and root password

There are two way to change the mysql user and root password

mysqladmin
If you have never set a root password for MySQL, the server does not require a password at all for connecting as root. To setup root password for first time, use mysqladmin command at shell prompt as follows:

$ mysqladmin -u root password NEWPASSWORD

However, if you want to change (or update) a root password, then you need to use following command

$ mysqladmin -u root -p oldpassword newpass

Enter password:
Change MySQL password for other user

To change a normal user password you need to type (let us assume you would like to change password for nikesh):

$ mysqladmin -u nikesh -p oldpassword newpass

Changing MySQL root user password using mysql sql command
This is another method. MySQL stores username and passwords in user table inside MySQL database. You can directly update password using the following method to update or change password for user vivek:

1) Login to mysql server, type following command at shell prompt:

$ mysql -u root -p

2) Use mysql database (type command at mysql prompt):

mysql> use mysql;

3) Change password for user nikesh:

mysql> update user set password=PASSWORD("NEWPASSWORD") where User='nikesh';

4) Reload privileges:

mysql>  flush privileges;
mysql> quit