Can we change graphic card in a laptop?

It's possible, but it would be best to take the laptop to someone who knows what they're doing. Or, you could build your own laptop and decide exactly what you want based on how much you are willing to invest.
It's never been more affordable to build your own PC. If you are good at managing your budget it could be more affordable than buying a new PC from Best-Buy or Wal-Mart.