Can I change my processor and video card in lenovo g40-30 laptop?

Or if not, what else can I change to improve my gaming experience?

No. The Video chip of a laptop can never ever be changed.

This is because in most cases they are soldered onto the System-Board.

In some Laptops only, the CPU could be upgraded (provided that they are installed in a CPU Socket).

You can Increase the RAM, install driver updates for everything else.Update the BIOS etc.

Finally you can hope that such few updates / upgraded can improve you gaming experience.

Otherwise you are looking at spending about $ 50-800 to get a new 'gaming' laptop.

There are many things - more ram, less junk on your hard disk, a decent antivirus, no external drives plugged in. If you have vista its really slow so change it - update all your drivers. Then run clean up defrag and antivirus full scan.

If that doesn't work you need a new machine.

No!