If you are using the integrated graphics on the motherboard, then that is the reason why it lags. The game is fairly old, but so is the integrated graphics on that motherboard. I think the integrated graphics are amd hd 4200, which was low end when that generation was out and is still a low end gpu for gaming.
Going to something like a 7770 or r7 250x, or 750 ti will improve the quality quite a bit for around $100-120 ish. Something like a 270/270x or gtx 760 will last a while and play modern games alot better.