WordPress themes come in the form of a .zip file. Upload your Zip file without extract.
In order to change your theme click on appearance in the left hand side like seen below.
Once you click on themes, you will see an “install themes tab” this will give you several options, whether you already have a theme or you want to find a new theme.
If you already have a theme that you have either purchased or downloaded somewhere else, just his the “upload” button and you can search for the file location where it is stored on your computer. Be sure to upload your theme as a .zip file.
If you need to find a theme, you can search by categories or select some of your desired features further down the page. Just select the one that you like and it gets added to your themes directory.
Finally, once your theme is either added or uploaded, you will need to activate the theme to make it live on your site. Before you do that, you can hit preview and a preview box will pop up allowing you to get a feel for how it looks before it goes live to everyone else. If you are ready for it to go live, click “activate.” What is great is that all of your old content will still appear even once you switch to a new theme.
This video will show how to activate a new theme once you install it.