1 Have you made sure that there are no other programs running while you are playing? If any are, even in the background, that can cause problems.
2. Do you regularly reboot (power off and back on) or just power off the computer? If not I would suggest doing so as that is the only way to get back all resources used. Just closing programs doesn't do it.
3. Have you checked the system for overheating? That can cause it to lag and, if not fixed, cause hardware damage. Try installing a temperature monitoring program and see what the temps are when you are and when you aren't playing.
If they are high, then you need to start by cleaning out the laptop (inside) of dirt, dust, debris, etc. Then, if needed, replace the thermal paste. Also if any fan is not working as it should that would need replacing. Then you can consider other cooling options, if necessary.
4. Should you not feel comfortable doing the work yourself try having a local tech look at it. Unless it is under warranty, then contact the manufacturer.