Easy breazy, assuming you really are using the latest and greatest (which would be 2.4.1 at this moment). Go to Global settings -> Files and check the box for "Enable skins directory". Then go to your Files tab and see if you have a selection in the drop-down menu for Skins. If so hit it and be amazed.

BTW I don't edit skin files this way. All I know is it's there and you can use it to edit files. I assume "folder permissions" stuff will come in to play in this situation and I'm tired of trying to figure that stuff out. My host is cool. I can do stuff without CHMODing files, but that happened after someone maliciously did malicious stuff to my media folder.

Anyway if you want to be able to edit skins through the back office then there ya go. Personally I find using a 'syntax enabled' editor and an FTP program much nicer, but hey to each his or her own yah?

Hi !
Thanks for prompt answer. Yet I'm still a bit lost.
I'm not too sure where i'm at in the file system/media library and all (sort: I'm in the house but where ?)
I somehow got into the media library, uploaded the css I needed, can access it for modifications. How can I put it back into the right skin folder and view the changes ?
Or should have I stayed away from the media library ?

Precision: I did install the latest stable version ! 2.4.1.

I did chance upon the "special folder"/skins menu... Great ! Will fiddle with this, get confidence in css and maybe end up following your advice.
Thank you very much.