The author of the blog post decided to upgrade their Hugo version from 0.40 to 0.135, despite the old version working fine. They documented the changes they had to make during the upgrade process, which included replacing template calls, updating page references, and flipping the meaning of "next" and "previous" in their theme. The author also had to update their Markdown files to work with the new Goldmark renderer, which replaced the old Blackfriday renderer. This involved making changes to how they wrote Markdown, including mixing HTML and Markdown, using angle quotes, and indenting nested lists. The author also had to configure the Goldmark renderer to turn off code highlighting and use the old method for generating heading IDs. They wrote a script to compare the output of the Blackfriday and Goldmark renderers and used it to identify and fix issues with their Markdown files. The author notes that the upgrade process was time-consuming and not without its challenges, but ultimately thinks it was worth it to have a more future-proof Markdown renderer. They also mention that they will likely have to make similar changes when upgrading their other site, wizardzines.com, which is still using an older version of Hugo.