Shapes are defined in an xml file which can be edited with a plain text editor as described in the macros section. This file is named shape.xml and is located in the FixtureLibrary which lives in %programfiles(x86)%\Avolites\Titan\FixtureLibrary (PC Suite) or in D:\TitanData\FixtureLibrary (consoles). Please note that this folder is by default hidden and marked as system. You can access it by changing the folder options, or by typing D:\TitanData into the explorer address bar (don't forget to click Pause when using the internal onscreen keyboard).
Since all shapes are defined in one single file, editing this file must be done with great care. One false item, one sign in wrong place may render the entire file invalid, and no shapes are available inside Titan until the file is fixed.
As like as macro files, the shape file is read upon software start. After applying changes you need to restart Titan in order to make changes effective.