If I install \upgrade windows8.1 on windows 7 Enterprise X64 bit OS it will upgrades? So I can able to use all installed applications which was installed windows 7 X64 Enterprise

Hi raveena-tendon,

Upgrade from Windows 7 to Windows 8.1, the personal data can be kept. As for the applications and the settings, I am afraid it is not available.

Here is a link for reference(Pay attention to "Windows 8.1 Supported Upgrade Paths" part ):
Windows 8 and Windows 8.1 Upgrade Paths
https://technet.microsoft.com/en-us/library/jj203353.aspx#EightOne

Best regards