How to install a theme in Magento 2
Installing a theme manually
Download the archive that contains the new theme. Unzip it and use a file manager like FileZilla to upload the files to the public root directory of your Magento 2 installation.
Your next step is to log in to the server using SSH. When it’s done, run two commands in the command line order. The first command upgrades the setup, and the second one deploys the static content.
php bin/magento setup:upgrade php bin/magento setup:static-content:deploy
Applying a storefront theme
Let’s imagine that somebody has installed a new Magento 2 theme for you. Your job here is just to apply it to the storefront.
Go to Content > Design > Themes to see the list of all currently available themes. Click the theme to manage its settings.
To apply the theme, navigate to Content > Design > Configuration. Select the Store View and tap ‘Edit’.
Select the Theme you want to use and click the ‘Save Configuration’ button to activate it. That’s it!
Putting a new theme to use is a little bit more difficult task since you need to install it first.