Question

As we humans are matter do we change into liquid and gas

Answer 1

Before moving to your question, lets briefly tell you about the human body.
The human body is a complex mixture of all phases of matter except plasma (the very hot stuff not the blood fluid) and including gas.
Bones are solid, blood is a mixture of liquid and mainly gelatinous red blood cells
Skin and flesh may seem fairly solid but are in fact a mass of cells of many types.
But as Sean Ridout says it does not make any sense to try and say, even on the molecular level, that a human is solid or gelatinous or whatever.
A lot of the macromolecules in a human body if extracted and purified can be crystallized but they behave totally differently when in the cells and fluids of the body.
So human body is a combination of solids, liquids and contains gas too!!

Now, your question is do we change into liquid and gas. So only considering as a matter,
roughly answer is "yes". But can you do it to your body? NO (Beacuse you will dead)

We can heat ice(solid form) and it turns to water(liquid form). If we cooled again it will again return back to solid form (ice). So it is called reversible process. Also, an irreversible process is a process that cannot return both the system and the surroundings to their original conditions.

We can transform the human body into a liquid using some complex techniques or gases by burning it at a higher temperature. This is an irreversible process. So we cannot come back to original state. (Also as we all know, this cannot be done for a living body!)

Example: "cremation", the disposal of a dead person's body by burning it to ashes, typically after a funeral ceremony.