This feature Works only in surface mode so you need to switch to the surface mode and you can see that new buttons have appeared in the toolbar.
UP Step UP with the multiresolution, and add the new subdivision layer if you are on the highest one.
DOWN Step DOWN with the multiresolution (if it exists).
If we click one of them to 3DCoat offers us to open the multi-resolution panel.
If we click yes then the multi-resolution panel will open and also you can find this panel among the Windows menu> Panels tab.
