I just renamed the old theme folder via ftp, uploaded the updated theme to a folder with the original name and voila! Deleted the renamed folder after I checked all the pages, job done :)
Though I’m confused, where do I find the update? If I follow the link from the automatic email about the update it just prompts to download the same theme version number file I already have?
This is mentioned in the documentation provided with the original download, which looks to involve a backup then uploading the new theme files to the original location via ftp.