This will also answer the question 'How to uninstall MySQL as a service'.

If you want to save your exisiting databases then goto 'C:\mysql\data\' and copy all the sub-folders in there that you want to keep, and paste them into a temporary location. Once your new installation is up and running, you can copy them back into 'C:\mysql\data\' ready for use. Note that this is not exactly the same as the 'upgrade MySQL' method on the mysql website, but works for me.

Whether you have saved your old databases or not, the next step in removing MySQL is then to delete the folder 'C:\mysql\' and all its containing sub-folders. Then , to remove the service, goto a DOS box and type 'mysqladmin -uroot -p shutdown' , type your master password if it asks for it. Type in 'mysqld --remove' and this will uninstall and remove the service.

You are now safe to proceed to install your new version.

IF you have any problems installing as above or for any other queries then you might find the MySQL section of our forums very helpful.