The installation of a new template in Drupal is very similar to the one for a module.
Step 1: Once you are in the administrative area of your Drupal application go to Appearance > Install new theme.
Step 2: On the new page you are given with two options:
(i) via direct link to the desired theme
(ii) upload it from your local device
Step 3: When you are ready with that, click on the Install button.
Step 4: After the installation of the new theme is completed click on < Enable newly added themes > and scroll to the bottom of the page where the Disabled themes section can be found.
Step 5: Once you find the new theme that you have just installed, you can activate it via the Enable button