It depends on your Motor KV, Higher KV normally draw higher Amp and require Bigger ESC. You can refer to Most Brushless Motor Technical Spec. and see the Max. Amp correspond to KV. If your motor now is 1900kV should be handle 4S means 2x2cell in series got 15.6V (Max 16.8V in Full Charged). and Running in 1900x16.8 Max 31920rpm.
If you try 2x3cell in series Max. got 25.2V and running in 47880rpm. If your motor power is small (I don't know your motor power KW), it will draw out High Amp and Overheat. so you better refer to your Motor Technical Spec. and see can it handle or not, then you can choose a Right ESC to fit for it.
Now if you try 120A ESC and 6 cell with it and notice the temperature. If too hot, try smaller prop. Or Try 5 cell. Using 2S and 3S in series (With Same Capacity and C).