To uninstall a MySQL where you have used the MSI packages, you must use the Add/Remove Programs tool within Control Panel. To do this:
Right-click the start menu and choose Control Panel.
If the Control Panel is set to category mode (you will see Pick a category at the top of the Control Panel window), double-click Add or Remove Programs. If the Control is set to classic mode, double-click the Add or Remove Programs icon.
Find MySQL in the list of installed software. MySQL Server is installed against major version numbers (MySQL 5.0, MySQL 5.1, etc.). Select the version that you want to remove and click Remove.
You will be prompted to confirm the removal. Click Yes to remove MySQL.
When MySQL is removed using this method, only the installed components are removed. Any database information (including the tables and data), import or export files, log files, and binary logs produced during execution are kept in their configured location.
If you try to install MySQL again the information will be retained and you will be prompted to enter the password configured with the original installation.
If you want to delete MySQL completely:
Delete the associated data directory. On Windows XP and
Windows Server 2003, before MySQL 5.1.24, the default data
directory would be located within the MySQL installation
directory. On MySQL 5.1.24 and later, the default data
directory is the configured AppData directory, which is
C:\Documents and Settings\All Users\Application
Data\MySQL by default.
On Windows 7 and Windows Server 2008, the default data
directory location is
C:\ProgramData directory is hidden
by default. You must change your folder options to view the
hidden file. Choose Organize,
Folder and search options,
Show hidden folders.