openup RazzArenaPak0.pk3 with winzip or winrar and browse to models\players\jazz\ and take a look at the tga files.

then copy/extract a set of .skin files and edit it and fill in the file names of your newly made skin.

create a new pk3(zip) file with the same folder structure (models\players\jazz)
in there put your new .skin files and the .tga files you made.

something like:

models\players\jazz\head_yourname.skin
models\players\jazz\upper_yourname.skin
models\players\jazz\lower_yourname.skin
models\players\jazz\yourname.tga

dont forget to rename the .zip to pk3 and yes you need to put it inside "razzdata" :P