Installer not removing previous versions in Windows c#

Question

Previous version of application is not removed when installing new version

When I try to install this on a machine which already had installed its earlier version...it gives me an error Message Like This...

"Anothe Version of this product is Already installed. Installation of this version cannot continue. To Configure or Remove the existing version of this product ,use ADD/Remove program on the Contol Panel."

What should i do, so that the installer either repairs or uninstalls and reinstalls it automatically?