Vocabulary question no. 20 - using a small oven

Hi,

I went to a Chinese restaurant yesterday. I tried something that is called hot pot. What we get is a small gas hob and a big pot divided into two chambers if I can call it like that. One is spicy, the other one is not.

Now, what do we say if we want to increase the strength of flame?

1. I want to increase the strength of fire.
2. I want to increase the strength of flame.
3. I want to turn up the fire.
4. I want to turn up the flame.
5. I want to turn up the strength of fire.

I don't know how native speakers say it.

Thanks in advance