Editing an existing STL file

I am a new Shapr3d user. Before attempting to make a new design I thought I might take an existing STL file I have purchased and carved on my CNC many times and simply change some of the characteristics of it. For instance, the design is for a spoon which I want to deepen the cup end and perhaps reshape the handle a bit. Is this possible using Shapr3d and is it more trouble than starting a new design altogether? Appreciate any comments.