uploading new theme to my site

I am a total beginner I have done a bit on wordpress sites but this is the 1st time i have made one from the start.

I brought a mojo theme downloaded it it has come as a zip file but i can not upload it onto my site I get this error
Installing Theme from uploaded file: jewelery-store-responsive-opencart-theme-theme-files.zip
Unpacking the package…

Installing the theme…

The package could not be installed. The theme is missing the style.css stylesheet.

Theme install failed.

can you help please ??