1. Login to your WordPress admin dashboard.
2. Under the dashboard menu, hover over Appearance and click on Themes.
3. Click on Upload Themes.
4. Click on Browse and choose a theme compressed in a ZIP file from your PC/Laptop. If your ZIP file contains a folder like an 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 a theme, and then if it is successfully installed, it will show a message as a Theme installed successfully. Now click on Activate.
Congratulations, you manually installed and activated a new WordPress theme.