Hi wanda578,
Thanks for visiting Apple Support Communities.
If you're unable to install or update iTunes due to an issue with the Apple Mobile Device Service, I'd suggest trying to restart it by following the steps in this article:
How to restart the Apple Mobile Device Service (AMDS) on Windows
http://support.apple.com/kb/TS1567
If the issues persist, you may find the troubleshooting steps in this article helpful:
iTunes: Troubleshooting security software issues
http://support.apple.com/kb/TS3125
Best Regards,
Jeremy