Every time i start to download the 8.1 update it says to me you need to use an account with adminstrator privilge.So what i do for that and thank you for the respond.

Have you signed in to your Windows 8 as an administrator user?
If you have not signed in to your Windows 8 as an administrator user I would suggest you to sign in to your computer as an administrator user and then try to upgrade to Windows 8.1.
To know more about administrator account please refer to the section What's a user account? of the link given below.
User accounts: frequently asked questions

http://windows.microsoft.com/en-ca/windows/user-accounts-faq#1TC=windows-8

If you have already signed in to Windows 8 as an administrator user and then also its asking you to sign in as an administrator user then I would suggest you to follow the steps given in the link given below.
Why doesn't Windows 8.1 think I am an Administrator

http://answers.microsoft.com/en-us/windows/forum/windows_8-windows_install/why-doesnt-windows-81-think-i-am-an-administrator/306e375a-1a93-4288-a085-ebd3bcef29bb

You can refer to the link given below for more information for the upgrade to Windows 8.1.
Update to Windows 8.1 from Windows 8

http://windows.microsoft.com/en-ca/windows-8/update-from-windows-8-tutorial