Why i can not install the new version of itune to my desktop

Try repairing Apple Software Update from the Programs and Features control panel, then uninstall it before trying to reinstall iTunes. If it won't repair try the MS install & uninstall utility mentioned in note 1 in the following guide.

For general advice see Troubleshooting issues with iTunes for Windows updates.

The steps in the second box are a guide to removing everything related to iTunes and then rebuilding it which is often a good starting point unless the symptoms indicate a more specific approach. When reinstalling right click on the downloaded setup file and use run as administrator. It may also help to temporarily disable any non-Microsoft anti-virus.

Review the other boxes and the list of support documents further down the page in case one of them applies.

The further information area has direct links to the current and recent builds in case you have problems downloading, or want to revert to an older version if the current one won't work properly for you at the moment.

Your library and device backups should be unaffected by these steps but there are links to backup and recovery advice should it be needed.

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Here: iTunes - Download iTunes Now - Apple

Try following the steps here: If you can't install or update iTunes for Windows - Apple Support

and here: Troubleshooting issues with iTunes for Windows updates