Step 1: Log in to your admin section. It is available at https://your-ghost-blog.com/ghost.

Step 2: In the Ghost Admin, go to Settings → Design & branding

Step 3: Click Change theme. It will open a modal window.

Step 4: Click on the Upload theme button, and select the flux.zip file.

Step 5: After the upload is complete, under Installed themes click Activate.

That’s it! Now you can start customizing your theme.