すると・そうすると: the difference
するとN3
Meaning
Having done..., If...is done...,
Past papers
Tested 5 times in past papers
Example
口笛を吹いた。すると、小鳥がやって来た。
I whistled, and a little bird came.
そうするとN3
Meaning
Having done that..., If that is done...,
Past papers
Example
もう少し音量を上げて。そうするとみんな聞こえるから。
Turn the volume up a bit more. Then everyone will be able to hear.
How to tell them apart
「すると」 can describe something that already happened or draw a conclusion; 「そうすると」 leans toward 'if you do that', and shows up in instructions and when discussing solutions.
The result here is also something that simply follows, so it normally isn't an order or a request.