There are 2 method to Install Theme, Installation via WPAdmin Panel or Installation using FTP
1.Wordpress.org
You can download free themes directly to your WordPress installation by using the Add New Theme option in the Appearance sub-menu.
OR Use Manual Method (Themes unavailable via WordPress.org):
Click on Uploads => Upload Theme and Browse the downloaded zip file from the desktop where you have it downloaded
Go to website https://gutenify.com/ to download theme
After you select theme, go to that theme page and then click on “Download Now” button to download theme zip file
Log in to the WordPress Administration Panel
Go to Appearance => Themes =>Add New