On the few refrigerators with that type of dial I've used, a lower number is warmer because you are sliding/rotating the numbers toward the 'warmer' side of center. Conversely, by sliding/rotating the numbers toward the 'colder' side of center you're setting the thermostat lower, which is labelled with higher numbers.
Again, I've only encountered a few such temperature controls. They were mostly owned by older relatives. However, they all worked the way I've described.
That said, we've members here with much more experience with such equipment than I do. While you're waiting for others to chime in, I'd put a thermometer in the 'fridge to get a starting point: '2' = __?__F. Assuming that's a stable temp, rotate the dial to '4' and note if the compressor runs more often and/or the temp drops.
Hope this helps.