There are two places that you can officially get PressWork. The first is from the WordPress.org theme directory. The other is from http://presswork.me. If you have downloaded PressWork from another site, I really recommend deleting it and getting an official version from one of the two places mentioned above.
The .zip file
If you have downloaded PressWork directly to your desktop, you should have a .zip file. If your system prompts you to save or open the .zip, be sure to just save it to your desktop. If your system automatically unzips the file, you will need to zip it again to upload it using the WordPress theme uploader.
The WordPress Theme Uploader
You can totally bypass having to download the theme to your desktop by installing it directly from your WordPress wp-admin. Go to Appearance -> Themes and click on the Install Theme tab. Now search the WordPress.org theme directory for PressWork and click “Install”.
To upload the theme from your desktop, all you have to do is click on the Upload link near the top of the Install Themes page and browse for the file. Select the file and then click the Install Now button. The theme will now install itself in the appropriate place. Note that the file you upload must be a .zip file or it will not work properly.