Question: I have Flash files that I would like to make edits on but I don't know how or with what.

Is there some software that can edit a Flash (.fla) file?

(Ideally something free.)

Answer: 
You can download the 30-day trial version of [Adobe Flash Professional](http://www.adobe.com/products/flash/). I don't know of any free alternative that works as well.
From the command-line, you may try [SWFTools](http://www.swftools.org/) - SWF manipulation and generation utilities

You can install SWFTools distribution (which has also a command line program), and use [SWFExtract](http://www.swftools.org/swfextract.html), that can decompile flash files.

On OSX, install via: `brew install swftools`.