Most programs and applications use an installation program to also uninstall the same programs. Very few have a seperate uninstaller to the installer.
What you're getting is due to the fact that you're running the installer to uninstall, which is perfectly natural in most cases. But this uninstaller/installer detects the version installed and stops when it finds the same (or better) is installed already.
Hopefully another member can provide steps to help you further, but I'd suggest taking a look at the Sun website to find your version, and to see if there are any other uninstallation instructions.