Based on the quick start template for Hugo theme Stack. It uses Hugo modules feature to load the theme.

Update theme manually

Run:

hugo mod get -u github.com/CaiJimmy/hugo-theme-stack/v3
hugo mod tidy

This starter template has been configured with v3 version of theme. Due to the limitation of Go module, once the v4 or up version of theme is released, you need to update the theme manually. (Modifying config/module.toml file)