Oh, I already got help and forgot to edit the thread

I just added a modifier 'Decimate' and went to Un-Subdivide.
It works now.

So I was making a hat[filesmelt.com] for Garry's Mod and was just about to test it out in-game when I got this funny error while compiling on GUIStudioMDL 2.2:


Apparently models for source games aren't suppose to have more than 32767 vertices,
so how to turn my model 'simpler' again? Without redoing the entire hat..