First you are going to upload the theme folder. Inside the ZIP folder you downloaded you will see a folder named “theme.” Within it is a folder named “Nova.” Via ftp, upload the “Nova” folder to your WordPress themes directory. Depending on where you installed WordPress on your server, the wp themes folder will be located in a path similar to: /public_html/blog/wp-content/themes.
Next you need to select Nova and make it your default theme. Click on the design link, and under the themes tab locate Nova from the selection of themes and activate it. Your blog should now be updated with your new theme.