[YOUR HOME]/.Library/Application Support/Quake3/q3ut4/q3config.cfg
Library is a hidden folder, the one inside your Home Folder at least, so in order to go there simply make sure your top bar is showing the Finder options, then click on the "Go to" from the menu above (it should be next to "View"), and select "Go to folder...". A pop-up will appear, paste "~/Library" without the quotes and the folder will open, from there browse normally. :)
This post has been edited by Kolossus: 19 January 2014 - 02:34 PM