1. Login to your WordPress admin dashboard.
2. Under the dashboard menu, hover your mouse on Appearance and then click on Themes.
3. Hover your mouse on a theme that is not active and unused, or you wish to remove that theme. It will show you the option Theme Details. Click it.
4. A simple window will open. You can see the Delete option at the bottom area on the right side of the window. Click it!
5. A confirmation window will open. Click OK to remove your theme.
The theme is successfully removed!