ACP > Skins > (skin) > Global Config holds the skin's own settings. They're different in every skin. Elastic 2, for example, has:
Click ? next to a setting for its help. Change what you need, and click Save Changes.
The Style tab changes the skin's CSS without editing files:
Reset Skin Style removes all your style changes and goes back to the skin's own CSS.
Your changes are saved in the database, not in the skin's files, so a skin update doesn't remove them. They're also copied when you clone the skin.
The Language tab lists every piece of text the skin shows, such as headings and button labels. Search for the text, change it, and save. To translate the whole site, see Translate Jamroom into Another Language.