How do I upgrade my MacBook Pro OSX 10.6.8 to 10.7.5?

If your Mac has a Core Duo CPU, you can't.

If your Mac has a Core 2 Duo or better CPU, click here. Back up your data and check your applications for compatibility before upgrading.

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If you are preparing for MacOS Sierra ( release date 10/20/16) you need the following:

According to Apple, the official compatible hardware list of Macs capable of running Mac OS Sierra 10.12 is as follows:

• MacBook Pro (2010 and later)
• MacBook Air (2010 and later)
• Mac Mini (2010 and later)
• Mac Pro (2010 and later)
• MacBook (Late 2009 and later)
• iMac (Late 2009 and later)

This list of supported Macs is offered directly from Apple, shown during the MacOS Sierra debut presentation at WWDC 2016 conference. And you must be running at least OS X 10.7.5 http://www.apple.com/macos/how-to-upgrade/

http://www.apple.com/shop/product/D6106Z/A/os-x-lion