Updating a theme in Publii is a very simple process.
In this video, I go through a step by step process in how I perform this action.
It is all based on the excellent documentation that Publii provides.
If you rather learn by watching then reading a set of docs, than this video was designed for you.
Publii is a Static Site Generator that is designed for both a developer and a non coder to use.
I myself have used awesome SSGs such as Hexo and Hugo, and find that I can still build a SSG website that is extremely fast in less time then a conventional static generator.
For a non coder:
No security issues like WordPress