Un-installing PenPusher is generally handled by the normal Windows un-install applet through the Control Panel.  In some circumstances the un-installation information can be corrupted resulting in the software unable to be removed.  In these circumstances you should use Microsofts MSI Un-Installer package found at the following link :-

http://download.microsoft.com/download/e/9/d/e9d80355-7ab4-45b8-80e8-983a48d5e1bd/msicuu2.exe

Ensure that you un-install both the PenPusher and Anoto PenDirector components before trying to re-install. You will need to reboot your PC before re-installing the latest version of PenPusher / PenDirector and you should also reboot following installation.