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 Dell Webcam Central 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 Dell Webcam Central application and click on Uninstall.
After that, visit Software Informer review page of the product in order to obtain a link to the official download, press the green Download button, save the file to your computer and install it following the provided instructions. This should fix your problems.