Start Menu -> Control Panel -> Administrative Tools -> Services
Then find the MySQL service in the list, and stop it.
If your server is not running as a service, you may need to use the Task Manager to force it to stop.
Create a text file and place the following command within it on a single line:
SET PASSWORD FOR 'root'@'localhost' = PASSWORD('MyNewPassword');
Save the file with any name. For this example the file will be C:\mysql-init.txt.
Open a console window to get to the DOS command prompt:
Start Menu -> Run -> cmd
We are assuming that you installed MySQL to C:\mysql. If you installed MySQL to another location, adjust the following commands accordingly.
At the DOS command prompt, execute this command:
C:\> C:\mysql\bin\mysqld-nt --init-file=C:\mysql-init.txt