The most straightforward way is to jump into the game console (with the ~ or ` key depending on your keyboard) and lower values like "mat_picmip" to 2 or 3, "r_drawspecificstaticprop 0" to disable static props, and "cl_ejectbrass 0" so it doesn't generate shell casings. You can also mess with the "config.cfg" file in the game folder and change the resolution to something lower, set "fps_max" to whatever you want (like 30 or 60), and reduce render distance with "r_worldlights 0". If your integrated graphics card is still giving you trouble, just play in windowed mode at 800x600 resolution or lower - a lot of old Source games run decently that way and you'll get a decent performance boost.