When I try, it says the source file is not available. So I have tried "Repairing" the file and the same message. I went back to the orginal Installer file (*.msi) and tried reinstalling it. It says there is an older version running.
... Not sure if you've tried this already, but just in case ...
Unfortunately, this sort of trouble has gotten more complicated to deal with ever since Microsoft pulled the Windows Installer CleanUp utility from their Download Center. First we have to find a copy of the utility.
Let's try Googling. (Best not to use Bing, I think.) Look for a working download site for at least version 3.0 of the Windows Installer CleanUp utility. (The results from mydigitallife and Major Geeks are worth checking.)
After downloading the utility installer file (msicuu2.exe), scan the file for malware, just in case. (I use the free version of Malwarebytes AntiMalware to do single-file scans for that.)
If the file is clean, to install the utility, doubleclick the msicuu2.exe file you've downloaded.
Now run the utility ("Start > All Programs > Windows Install Clean Up"). In the list of programs that appears in CleanUp, select any Apple Mobile Device Support entries and click "Remove".
Quit out of CleanUp. Restart the PC, and try another iTunes install. Does it go through properly this time?
Control Panel --> Uninstall a Program
Right Click Apple Mobile Device Support --> Change
A window will pop up asking if you want to Repair or Remove. I said Repair
Once its finished repairing, go back to Control Panel --> Uninstall a Program
Double click or right click, uninstall Apple Mobile Device Support.
It showed up after it said it finished the install but when I right clicked on it windows said it was already uninstalled and removed it from the list.