You have downloaded a new theme from a trusted website and want to install it on your WordPress site using the Wordpress Admin area. If thats the case, follow this tutorial.
1- Login to your WordPress admin dashboard.
2- Under the dashboard menu, hover over Appearance and click on Themes.
3- Click on Upload Theme.
4- Click on Browse and chose a theme, which is compressed in a ZIP format file, from your PC/Laptop. If your ZIP file contains a folder like upload, first extract the content of uploaded files and the compressed theme file. Click on Install Now.
5- It will take a few minutes to upload the theme, and then, if it is successfully installed, it will show a message like Theme installed successfully. Now click on Activate.
Congratulations, you manually installed and activated a new WordPress theme.