Themes define the look and feel of your WordPress site. Changing a WordPress theme doesn’t change the content of the site. You pages and articles remain intact. It’s the design that changes. The following take you through choosing a theme. 

Step [1] − Click on Appearance → Themes as shown in the following screenshot.

Step [2] − Click on Add New.

Step [3] − Hover your mouse pointer over a desired theme and click Install.

Step [4] − Click on Activate.

You can now visit your site to view the changes.