Hi,
My guess is you are not editing the right file. Skins are located in 2 places. If you read the documentaion:
http://www.mojoportal.com/creatingskins.aspx
you will see the correct location to find the skins used by your site is under
/Data/Sites/[SiteID]/skins
rather than
/Data/skins
[SiteID] is usually 1 in a single site installation
Hop it helps,
Joe