Patricia, you can use virtually any graphics package.
The clothing is only 2D, it is just a matter of mapping an image to a layout.
If you look at the UVW png files, you will see the layout of each piece of clothing. It represents the full possible extent. If you lay your “cloth” on it, where there is no “cloth” the skin will show through.
To create a height map, which, gives your clothing more of a 3D look, the instructions are in the main topic.
I used the most basic of software (yes, I know, it looks like it, lol) and, of course, the better the software the easier it will be and/or the better quality you will obtain but you don't necessarily need high-end software.