I have got macbook pro 10.6.8 how can i install os x mountain lion on it?

You buy ML from the Mac Apple Store, download, install.

Use this link from another experienced user to create a copy of the ML install on a thumb drive before installing. Install deletes the install pack contnents, and you may want to restore ML from scratch and NOT want to download for 5 hours again:

https://discussions.apple.com/thread/3467451?answerId=16639520022#16639520022

Also, check this website for application that do not work on ML:

http://roaringapps.com/apps:table

AND ... have a good backup in case you want to go back to SL (it does happen) or in case you need to restores/restart due to einstallation error,

Check that your computer is compatible with Mountain Lion.

To check the model number hold down the option/alt key, go to the Apple menu and select System Information.

• MacBook Pro (Mid/Late 2007 or newer) model number 3,1 or higher

Your Mac needs:

• OS X v10.6.8 or OS X Lion already installed
• 2 GB or more of memory (More is better - 4 GB minimum seems to be the consensus)
• 8 GB or more of available space