Major Upgrade - not overwirting replacing current version on target machine

Hello,

Seems to be many questions on the internet on how to get this to work. We have tried:

Update version
Update Product Code
Update Unique ID (I think this is the Package Code?)
Setting upgrade paths from min to max (max being the last version out there that we want to have overwritten)

But when we install it increases the version number in programs (ie Add/remove programs list), but does not remove the current version.

Any ideas on what we are doing wrong. Just want to do a basic install with the current ver. on the target machine replaced with what we are installing....

Thanks
MLM