The best way to remove any WordPress theme from your website is to do it via the WordPress admin area because some themes have install hooks which will remove unwanted data from your database.
- Login to your WordPress admin area.
- Navigate to the Appearances -> Themes page.
- Select and delete the theme as required.
- Login to your hosting account via your cPanel or FTP.
- Locate your wp-content/themes/ folder and delete the existing PremiumPress theme.