what's the different between "switch" and "change"?

They’re sort of synonymous, but switch could imply two options, vs change having a multiplicity

switch is when you replace one option with another one that you identify.   "I used to use product a, but then I switched to product x."    it can also mean you exchange two things for each other.  "she agreed to switch seats with me so I could watch the takeoff." change is more general. all it says is that the original thing becomes different.  "I changed my hair colour."  

Semantically, switch has the implication of speed and/or very close proximity. For example it's picture day at a school and the photographer will say "can you two switch places?" The photographer may also say change places but usually if there is some distance. Switch would be for side-by-side change may be two different rows. Change is more expansive than switch. Also think about a light switch. What image comes to mind? Could we really refer to it as a light change?