Hi,
These are the steps that you need to follow:
1 - install the previous version of qtp ( 9.2 or 9.1) or whichever one you are using
2 - Download and install the installation cleanup utility from microsoft website and use it to uninstall the previous version of QTP.
Here's the link: http://support.microsoft.com/default.aspx?scid=kb;en-us;290301