Can we say that human species has conquered all the continents?
This depends on what it means to "conquer" every continent.
On the one hand, this is true. Human beings live on every continent of the world. There are large populations on six of the world's continents and a small population of researchers living in Antarctica.
On the other hand, you could argue that humans have not done this. You could argue that the human population of Antarctica is tiny and is not native to that continent. You could also argue that there are parts of every continent (such as deserts or tundra or high mountains) where it is very difficult or even impossible for human beings to live. You could argue that human beings have not truly conquered these harsh environments.
In this way, the answer to this depends on your definition of "conquer."