Help installing themes

I'm new to the opencart community and I need help installing themes.

I have already successfully installed opencart in my server, everything is working properly and now I want to install a custom theme, I decided to download "Black Diamond" and "Purple Theme" from the free extensions for version 2.0.2.0

I followed the instructions for both, which seems to be the same for any theme:

-Extract blackdiamond.zip and upload blackdiamond folder into “catalog/view/theme/” folder.
-Now log in into back office of your open cart.
-Click on System>Setting
-In right side corner Click on pencil icon
-Click on “Store” tab
-On “Template” option please choose “blackdiamond”
-Click on Save icon to save your setting
-Now you themes is installed.

After following the instructions, the theme is not loaded and the front page shows the default. What I'm doing wrong? Is there a missing step? Do I need to delete the default folder?

Thanks for any help or hints on how to install a theme.