A theme can’t be uploaded and installed on a WordPress.com hosted site. However, there are a lot of themes already available that you can activate. Also, with the Premium plan, you can use custom CSS to change the look of the theme.
If you really want to use the City Tours theme, then that involves registering a domain, buying hosting, and setting up a site using the free software from WordPress.org: https://wordpress.org/
If you decide to stay on WordPress.com, contact the theme seller about a refund.