Is there a way to change which LaTeX file is previewed? My project involves several documents

A project can only have one main file at present—it's the one which loads when you visit the document.

A simple way of compiling another file is to put:

\input{other-file.tex}

as the first line in the main file—before even the document class. This will cause us to compile that file instead, and LaTeX will ignore the rest of the "main" file.