How to set up a new theme

Step: 1

In your shopify Admin panel, under THEMES & SETTINGS section in the left sidebar menu, click on the "Themes"

Like this:

Step: 2

In this section click on the "Set up a new theme" button.

Like this: 

Step: 3

New page will open with all of the existing themes and  its installation setup.

Like that...

Step: 4

Chosse a theme a clicl on the "Run setup" button.

That's it new theme will be installed on the store.