Click the theme tab, then see the various options you have for themes.  You can either select an entirely new theme, or make tweaks to the current theme you are using.  You can upload a new logo to replace the one that is the default of this theme, upload a new icon, add custom CSS, change the text font, or tweak specific theme settings.  These settings have to do with placement of items on the theme (like primary / secondary links or whether or not to use a logo).

It is important to note that these settings are specific to this version.  If you duplicate this version, these settings will be copied over but you are effectively tweaking global default settings specific to this instance of the use of the theme.