I need to update my Mac OS x version 10.5.8 to support Itunes 10.7 but I can not locate where I can download the update.

Welcome to the Apple Support Communities

See if your Mac is supported > http://support.apple.com/kb/sp575 Buy Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard Then, make a backup, insert the DVD and upgrade. Finally, go to  > Software Update and install the most recent version.

See if your Mac is compatible > http://www.apple.com/osx/specs If you prefer, open App Store and purchase Mountain Lion. Check if your programs are supported > http://www.roaringapps.com

You need to install Mac OS X 10.6.8 to run iTunes 10.7.

Download iTunes 10.7 here: iTunes 10.7

To upgrade from OS X 10.5.8, you must first buy Snow Leopard on DVD disc. It is not available to download from any legitimate source.

Online (US): http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

Online (UK): http://store.apple.com/uk/product/MC573/mac-os-x-106-snow-leopard

Elsewhere: call the phone number in the Apple Online Store

Apple's price is $19.99 or £14.00.

Make sure your system meets Snow Leopard's requirements:

Mac OS X 10.6 "Snow Leopard" System Requirements

To install Snow Leopard for the first time, you must have a Mac with:

• An Intel processor
• An internal or external DVD drive, or DVD or CD Sharing
• At least 1 GB of memory (RAM) (additional RAM is recommended)
• A built-in display or a display connected to an Apple-supplied video card supported by your computer
• At least 5 GB of disk space available, or 7 GB of disk space if you install the developer tools

After you install Snow Leopard you can decide if you want to upgrade OS X to the latest version, Mountain Lion. Mountain Lion is available in the Mac App Store, which is available to you after upgrading to Snow Leopard.

Note, G5 is NOT Intel.