He just said he has mxm2.. so clearly he can ''upgrade''..
Anyways back on topic.. NO.., you cant if i recall correctly mxm2 has a max of 22 watts output, where mxm3 is around 35. It may physicly fit (wich i doubt) but it will not have the required juice, nor cooling for that matter.
But to be honest, when you buy a laptop you should not have bought it with the intention of swapping every part in it, if you did. you should buy a desktop