You can install a theme from WordPress, or upload a premium theme that you have purchased or received elsewhere.

Navigate to your WordPress Admin area.

From the Appearance menu, click Themes.

Click the Add New button.

Using the search bar, browse for the theme you wish to install.

Hover over the preview of the theme and click Install.

Note: Optionally, if you purchased or received a third-party theme you want to use instead, click the Upload Theme button. Browse to the theme's files on your computer, and click Install Now.