When I click on the left menu on Faces > Smooth it's making smooth but kind of rounded:
I want to keep it sharp as it was in the first screenshot but smooth.
I think what you mean is to make the top sharp, so to do that you need to create an edge loop (Ctrl R) Then orient the purple line so that it is horizontal. Left click, then move the line towards the top, it should smooth it out. If not you can reply
Smooth shading works by averaging the angle between two faces/edes/vertecies. This allows for smooth looks while keeping geometry low.
There are multiple ways to retain sharpness in a model: