i need help updating ios6 using itunes ?

If your iDevice is using a version of iOS lower than 5, you will need to use iTunes on your syncing computer to perform the upgrade. Use the Apple link below as a guide for the upgrade.

http://support.apple.com/kb/HT4972

Also read the instructions from the section entitled "Update your device using iTunes" at the link below.

http://support.apple.com/kb/HT4623

Information regarding transferring purchases from your iDevice to iTunes on your syncing computer can be found at the link below.

http://support.apple.com/kb/ht1848

One small addition to stedman1's suggestions:

You haven't told us what type of iPhone you have. If you have an iPhone 3G or original iPhone, you will not be able to update to iOS 6.