[IntoRain]

Go to the file manager to edit all files (from the control panel of your site's host, not from the site's admin panel).

To edit the theme, if you open the html of your site you'll see all .css files being used (if you allow users to change themes, the .css files might be different!). After that, go to the folder called templates and access the theme you want to edit, as well as the folder css for the menu's css. Since you mentioned the main theme, the .css files will be in templates/main/media/style-city.css and css/menu.css

To edit the text in the .php pages, you can go directly to the .php file (so for example if you are in the page yoursite.com/adopt, everything written on that page will be either in the file adopt.php or adoptview.php inside the view folder OR lang_adopt.php in the lang folder. If you are in yoursite.com/myadopts then it will be in myadopts.php or myadoptsview.php or lang_myadopts, etc...)