Hi the king,
Welcome to Geeks To Go,
I'd suggest checking temperatures. Try CoreTemp
. If they get high during graphics intensive gameplay, invest in a better cooling solution.
Open Task Manager and keep that open on the Resource Monitor, play the game. When you start to slow down during a firefight, alt tab back to Windows and have a look at what is using your system resources. Is the CPU usage high? Memory? Hard Drives? Network activity? Let us know.
Check to see if you have the latest drivers for your hardware.
Closing as many background tasks as you can. Especially those things next to the clock in the right hand side of the task bar. Obviously the Anti Virus and Firewall should be running but you might be able to close a few things off such as Windows Sidebar. I see you have Avast running, that is usually a good AV as far as resources go.
Lastly, lower the resolution in the games settings, lower shading, etc. This can help ease the load on your system.
I wrote a detailed guide HERE
on speeding up your system.