The MBP needs to be disassociated from the original owners Apple ID. The original owner needs to call Apple Care to request that. Or if you have a sales receipt that proves you legally have purchased the MBP they may do it for you.
Then the MBP needs to be wiped clean and the most recent version of OS X that shipped with the Mac installed using OS X Recovery. You can also reinstall the iLife apps, which you should accept into your Apple ID in the Mac App Store on the Purchaes pane.