Many have done this. Just share with us where you are stuck and what you have done so others can try to help.
Have you watched the instuction videos how to convert your DB from Seditio to Cotonti?
The skin you convert by just comparing the example skin included with the Cotonti CMS to your Seditio skin files and add,replace,remove tags where necassary.
<img src="http://www.armaholic.com/datas/thumbs/green-sea-battalion-uniforms-version-03-preview_4.jpg" alt="green-sea-battalion-uniforms-version-03-" />