3D camera zoom

I have a question about zooming in a 3d world.

My game is a RTS so top down view so do I just change the camera pos to make it closer to the world as I am now or is there a proper way to zoom in?

You can change the value of FOV (field of view) in your camera to achieve the zoom effect.
With that you don’t need to change the position of the camera.

Note that changing the FOV will change the apparent distance between objects, and perhaps distort perspective. If you want to keep the projection the same, you are best to move the camera closer to the target. If you play with it, perhaps you could use a combination of some FOV twiddling with a camera move. It all depends on what look appeals to you.