Adding New Themes from the WordPress Admin area
The initial install is done from your admin menu:
Appearance > Themes > Install Themes > Upload > Navigate to the theme zip file you downloaded > Install and activate.
(if you’ve purchased a bundle, make sure to unzip this first).
(if you’re getting an error, you need to delete out the previous version first which can also be done under Appearance > Themes by switching to a different theme (temporarily) and then deleting out your theme in order to install the new version).
Adding New Themes Manually (FTP/SFTP)
To add a new Theme to your WordPress installation, follow these basic steps:
1. Go to https://wordpress.org/themes/ and choose a suitable theme for you.
2. Download the Theme archive to your personal computer/Mac and extract the files it contains. To be on the safe side it is recommended that you extract the contents from the .zip file. Do not just Open the file and drag the contents. Sometimes that will work, other times it will not. It will be more reliable if you extract the content. Depending on your operating system, you may be able to right click or control+click the .zip file and select Extract, Extract With, or Open With. Usually that will use or direct to your utility that’s used for extracting. Extract the files to somewhere that’s easy to locate, eg: desktop.
3. Using an FTP/SFTP client (like FileZilla http://filezilla-project.org/) to access your host web server, FTP/SFTP (upload) the folder contents to the wp-content/themes directory provided by WordPress. For example, a Theme named Twenty Fourteen should be in wp-content/themes/twentyfourteen. Follow the instructions below for selecting the new Theme.
4. Log in to the WordPress Administration Panel.
5. Go to Appearance > Themes
6. From the available themes section (Manage Themes), click on the Theme title (or Theme screenshot) for the Theme you wish to activate.
7. A preview of the Theme will be shown.
8. To activate the Theme click “Save & Activate” “Theme Name” link in the top left. Your selection should immediately become active.
Note: If the Theme preview is blank, do not activate the new Theme without investigating further. Your site may not be displayed correctly or you may have a corrupt download.
Or while in the Themes panel, just select “Activate” under the corresponding theme that you wish to use.