How I can upgrade mac os 10.5 to 10.8

Customers can still purchase Snow Leopard from Apple's online store's telesales agents.[1-800-MY-APPLE (1-800-692-7753) or Customer Service and Sales Support at 1-800-676-2775.]

Once you have upgraded to Snow Leopard you will need to download and install the Mac OS X 10.6.8 Update Combo v1.1. You can then access the App Store where you can purchase and download Mountain Lion.

Be sure your computer meets the minimum requirements:

Apple - OS X Mountain Lion - Read the technical specifications.

Macs that can be upgraded to OS X Mountain Lion

1. iMac (Mid 2007 or newer)
2. MacBook (Late 2008 Aluminum, or Early 2009 or newer)
3. MacBook Pro (Mid/Late 2007 or newer)
4. MacBook Air (Late 2008 or newer)
5. Mac mini (Early 2009 or newer)
6. Mac Pro (Early 2008 or newer)
7. Xserve (Early 2009)

Snow Leopard General requirements

• Mac computer with an Intel processor
• 1GB of memory
• 5GB of available disk space
• DVD drive for installation
• Some features require a compatible Internet service provider; fees may apply.
• Some features require Apple’s MobileMe service; fees and terms apply.

You cannot install the 10.6.8 update until you have installed Snow Leopard. I stated this earlier:

"Once you have upgraded to Snow Leopard you will need to download and install the Mac OS X 10.6.8 Update Combo v1.1. You can then access the App Store where you can purchase and download Mountain Lion."

You must first purchase the Snow Leopard DVD in order to upgrade from Leopard.