Sample Child Theme
If you are going to be making advanced edits to the OnePress theme, the best way is via a child theme.
Luckily I’ve already created a nice sample child theme for you.
Simply download the zip and upload the onepress-child-master.zip under your WordPress dashboard at Appearance > Themes.
IMPORTANT: Switching To Child Theme Notice: If you have NOT been using a child theme and are going to switch to one now, it’s very important to realize that all theme mods (Customizer settings) are saved in the database under a table using the name of your theme, so if you switch to a child theme you won’t lose your settings but they won’t apply. So you need to go WordPress dashboard > OnePress Theme > Recommend Actions to copy all the Customizer settings from original theme to the child theme: