In the fire demo there are several emitters, in order to simulate a big fireplace. For a candle flame, you only need one of these emitters.
But you have to change a bit the settings to reduce the random part: for example, you can try to bring force_min and force_max closer. This is because a candle flame is way more regular than a fireplace one.
But for better advices, please put the code you've already written, and a screenshot is possible.