When wordpress installed, there are few themes installed by default & they are Twenty Ten/Twenty Eleven. Login to your wordpress admin panel & access Appereance >> Themes.
Now, let’s see how to install the wordpress theme.
You will see two panes, Manage Themes & Install Themes. Manage themes is to manage already installed themes. You can activate, preview these themes.
To install a new one, click on Install Themes. You can search a theme OR upload it from your desktop by clicking on Upload themes. The downloaded theme should be in .zip format. Upload the theme and click on Install Now. Once installed, the newly installed theme will be available & you will be able to manage it accordingly.