I am using a WIndows 7 PC, with iTunes version 10.6.3. iTunes 10.7 update will not run.

My iPhone 5 will not sync because it states that I need to update iTunes from version 10.6.3 to 10.7. However, when I go to help in iTunes and select the 10.7 update nothing happens. No update. My version remains 10.6.3. Can someone please help me.....Thanks. I am running Windows 7 on a PC.