How to remove numbers from Menu Menu?

You have to use custom CSS to do that, here is an example code:

#sp-menu span.nav-counter {display: none !important;}

Add inside Template Options > Custom Code > Custom CSS or inside custom.css file.

 How to change the button Contact Us?

It's SP Page Builder Module published in "menu" module position. There are two modules, one published on the homepage only and 2nd on the rest of the subpages.

You can edit those modules and edit the Button addon inside, then translate the button text, change the design and update link inside, etc.