I searched past threads for my problem and found a bunch of them referencing the "Global Design Rule" as the window in which I need to set my desired track width. I tried inputting the value I wanted in "Minimum Allowed Values" but changing those just gave me error messages (something about the set track width beind smaller than the minimum track width). So I set the custom track widths to my desired value.
But whatever value I put it doesn't appear to update, neither in the 2D schematic, nor in the 3D viewer. The traces still show as being tiny. I ended up leaving too much spare space between my components, so I wanted to use thicker traces. Here are some screengrabs of my efforts:
As you can see I set the width to 2 mm, and those resistors are 1206 surface mounts, so the traces he ended up using are seriously tiny.
Also, this is my first time using KiCad, so it's possible I'm missing some obvious step.