the other thing that can cause slowdown on laptop are overheat...
try tilt it a couple degree so it will had some room for breathing (u can use eraser at the bottom or similar) or using cooling pad is advised.......
Almost impossible to changing GPU & processor on the laptop, usually they are soldered and bios locked..... (so they only works with original hw)
the common thing u can add/replace/upgrade is battery, Hard disk, or memory