Begin by downloading the theme’s .zip file from the source onto your local computer.
From your WordPress Administration area, head to Appearance > Themes and click Add New.
The Add New theme screen has a new option, Upload Theme.
The theme upload form is now open, click Choose File, select the theme zip file on your computer and click Install Now.
The theme is now ready to be activated from your admin. Select the Appearance tab and open the Themes directory, locate the theme and click the Activate link.