I'm new to dotnetnuke so I've a installed a ready made skin, similar to the design that I want to on  my site and I'd like to modify it slightly, rather than attempting to create a skin from scratch myself. I need to change the css on the main menu (to get rid of the background colour and border). From what I understand dotnetnuke skins need to be packaged with a manifest, in a particular way that I don't know. Since you can't upload skins that aren't packaged the write way, I tried to use the file manager to find the skin.css so I could download it, edit it and upload it again with the file manager. I managed to find default.css as well as portal.css. I'm getting very confused looking at all the different files. I've now set new skin as my skin at the portal level, so I  had thought that when I opened portal.css I would find the css presently used on my site, but there were no rules at all the whole file.
I have the skin.css on my desktop, which I could edit, but I don't understand where to upload it to. There is a skins folder in the file manager which contains about 6 other folders and I've no idea which one skin.css is meant to go in.
Any help would be appreciated. Sara