Hi @Omid Mohammadi,
Welcome to Microsoft Q&A!
Do you mean that the VS2015 can’t be launched after successfully installing it? Or does it crash when you install the VS2015?
If you have any anti-virus software or privilege management software, please temporarily disable them.
If it failed to install, please re-download the Visual Studio Enterprise 2015 with Update 3 from the page and move it to a clean folder in another drive.
Or try to put the installation file in root of C drive like C:\setup.exe and run it.
If you want to uninstall VS2012, you can go to Control Panel > Programs and Features > search ‘Visual Studio 2012’ > right click on it > select ‘Uninstall’ or ‘Change’.
If it doesn’t work, you can use the Program Install and Uninstall troubleshooter tool to uninstall it.
Sincerely,
Anna
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