When I select Themes under the MORE menu, I only see the default and I don’t see a link to the Marketplace.
How do I add Themes?
You have to turn on developer mode in the settings. (Advanced → Developer mode)
Once this is turned on a plugins menu will be available with a marketplace tab in it to install themes from.
Click plugins on the menu and then go to the marketplace pane and then click themes from where you can download. this is on the latest version