If you're upgrading from 3.x or older:

1. Upgrading will remove installed plugins, so make a list of the current state for later:

set --local plugins (read --null <~/.config/fish/fishfile)

2. Uninstall the old Fisher:

$ fisher self-uninstall

3. Install the latest Fisher and restore previously installed plugins:

$ curl -sL https://git.io/fisher | source && fisher install jorgebucaran/fisher $plugins