Hi Andy,
Are you using a Mac as well?
It’s much easier to save the .zip directly instead of extracting it, then compressing it again.
If you’re using a PC, you want to right click the download file, and choose “Save File As”.
If you’re using a Mac, you want to right click the download file, and choose “Download Linked File As”.
More info here: http://www.generatepress.com/knowledgebase/install-activate-addons/
Let me know if you need any more guidance.
Thanks!