For certain configuration settings you'll need to dive into the theme files and manually change code in there. There are two ways of doing this, one's more technical why the other one is easier to understand.
In order to do this on a self-hosted unit, you can access the files via SFTP. Finding the right folder can be tough sometimes. When using Digital Ocean you should be looking for a path like: /var/www/ghost/content/themes/sparox to get into theme files. There is documentation on how to manage files on your vps here: https://www.digitalocean.com/community/tutorials/how-to-use-filezilla-to-transfer-and-manage-files-securely-on-your-vps
When using Ghost Pro, the best option is to unzip the theme file, make the changes, then zip and upload it again. For most users this might be the best way of doing things, since using SFTP can easily become complicated.