How do you tell what WordPress theme you are using?
If your WordPress user account is of “administrator” type, the solution is easy; just head to Dashboard > Appearance > Themes.
If you don’t see Dashboard > Appearance > Themes, you may have an Editor or Author account, which can’t set or change the theme. In this case, visit your website’s home page, right click on an empty space and choose View Source. In the code that you see, press CTRL + F (on Windows) or CMD + F (on Mac), and search for “themes” without the quotes.
Look for a mention of https://www.yourdomain.com/wp-content/themes/your-theme/style.css, where yourdomain.com is actually your own domain name, and “your-theme” is the name of the theme you’re using.