You can customize most of the visual aspects of your website without editing a single line of code, using the live customizer from WordPress. From this page you can edit any primary aspect of your site such as logos, menus, colors, fonts and more.
To start customizing your website go to Appearance > Customize. From this page you can customize basically everything: logos, colors, design and more.
Changes not applied in preview
If you can't see the changes in realtime, this can be caused by a conflict between your website and your server.
In particular, the mod_pagespeed PHP module appears to be conflicting to the functionalities of the WordPress customizer.
To fix, simply copy and paste this code in the htaccess file of your wordpress installation
Once done, you can reenable pagespeed. To reenable pageSpeed, commend the second line with #