If you use Windows XP or below you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the Plascon Visualiser program and then click Remove.
If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the Plascon Visualiser application and click on Uninstall.
After that, visit the review page of the product in order to obtain an official link to download the latest version of the application. Click the green Download button, save the file to your computer and install it following the provided instructions. This should fix the issue.