This is actually from the “Common Problems” section of the first “Getting Started” chapter of your documentation:
Can’t upload theme
Problem: When you try to upload theme-name.zip through your WordPress dashboard in the way it’s described in the first installation video above and either it loads and loads with no result or you see the error message “Are you sure you want to do this?” followed by nothing happenning.
Solution: Many of our themes may contain many options resulting in additional images, files, etc, making the theme’s overall file size larger than many other themes you might have used in the past. If you’re facing this issue, it’s most likely because your web hosting account has PHP upload limits in place that are smaller than the size of the theme. So, if this is the case, the solution is simply to unzip the theme and upload it manually through your FTP program. This process is outlined above in the second installation video.
So, you just need to either increase your PHP file upload limit (which can also be done while you’re in that php.ini file) or just unzip it and upload the theme via FTP. Here’s that 2nd video from your docs that’ll show you how to do that: https://vimeo.com/16681592