Here it is almost 2 years later! did you ever get an answer? I have just borrowed one of these incubators from a friend.
On the top there is a butterfly wing nut - loosen it by turning it to the left, tighten by turning to the right. Sticking out above that is a screw thing with a flat top. Turn it left to make hotter, turn it right to make cooler. Make sure you have an accurate thermometer. I tried several and finally ordered one from Brinsea with a probe, accurate to within 0.1.
The thermostat will start and stop the heating element so it will range in temperature. My seems to have finally settled down to a range of 97 to 102. I am a first timer at incubating eggs so the average seems about right. It is important that this incubator is in a stable room temperature or the inside temp will fluctuate all over the place. I have a big disinfected rock inside mine to keep the temp more stable.