Installing from wordpress.org
Log in to your WordPress admin page, then go to Appearance and select Plugins.
To add a plugin, plugins click Add New. From this page, you have two ways to add a new plugin. If you know the name of the theme you want, search for it in the plugin directory.
Once installed, click the Activate link.
Installing from .zip file
Begin by downloading the theme’s .zip file from the source onto your local computer.
From your WordPress Administration area, head to Appearance > Plugins and click Add New.
The Add New plugin screen has a new option, Upload Plugin.
The Plugin upload form is now open, click Choose File, select the theme zip file on your computer and click Install Now.
The plugin is now ready to be activated from your admin. locate the plugin and click the Activate link.