Except WordPress Dashboard’s themes, you can search through the Internet and select another theme. It’s necessary to download it to your local computer and then proceed to upload it.
In most cases, the theme will be a compressed file such as .zip ot tar.gz format.
1) First, go to the WordPress Dashboard and log in.
2) Select Appearance and then click Themes.
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3) Choose "Install Themes" and click "Upload".
4) Select the "Browse" button and add the downloaded file from your computer. Then click "Open" and "Install Now". It will take several minutes.
5) When the upload process is complete, the following screen will be displayed:
6) Select "Preview" to load and see the new theme.
7) If you like it, then click "Activate".
8) Now, visit your site and the new theme will be displayed there. Congratulations!