Several of the themes offered by Moodle have forms that give the user options for different settings in the theme. None of the forms are the same. Different themes give you control over different settings. You will need to spend some time and explore your options. The Splash theme has a setting form for it, so let's take that as our example.
To view the themes with setting forms, go to the Site administration menu, select Appearance, and then select Themes.
In the menu under Themes, below Theme settings and Theme selector, you will see the list of the themes that offer forms which give the user a few more options to customize the theme. See the following image.
For our example, let's stick with the Splash theme. Select Splash from the menu.
You will now be on the Splash settings page. You will see that you have several options for customization here. You can link to a logo image, create a tagline, add a footnote, or add any...