how to install unity 3.5.0

hello sir,i try to install unity 3.5.0 but it oftenly says “you need administrator permission to acess” but am in administrator login only.What shall i do now.Please help me its an emergency

Try using right click “Run as administrator” or/and disable User Account Control (UAC).
How to disable UAC

In windows 7 or vista, you might have to right click the installer and choose “Run as Administrator”.