Why would you want to remove a theme?
- It’s buggy.
- You aren’t using it.
- Why leave a lot of code and possibly images you aren’t using that could bog your site down?
As long as you have the theme being removed saved somewhere on your local hard drive, you don’t need to worry about removing it. Just upload it later if you want to switch.
- Login to your WordPress site
- Typically sitename.com/wp-admin
- In the left hand menu, go to Appearance, Themes
- Hover over the theme you’d like to delete and click Theme Details
- In the bottom right corner, click Delete
- I would suggest repeating the steps above for every theme not in use.
Note: WordPress updates typically reinstall default WordPress themes. Don’t forget to go in and clean house after you update WordPress.