That file is your new binary Caddy binary, assuming your server is an x64 Linux machine.

Using that should follow mostly the same procedure as if you've built it yourself, following the doc @terribleplan@lemmy.nrd.li posted above, except you probably need to chmod +x that first, and maybe chown it too. (This is because your browser wisely does not mark files downloaded from the Internet as executable, and almost certainly does not run as root either)

Disclaimer: I've always used docker images instead and have not tested this. But I think it should work, assuming those docs are correct for the self-built case.

Move that file to your server (if necessary) and open a terminal in the directory where you've placed it. Then execute these commands:

chmod +x caddy_linux_amd64_custom
sudo chown root:root caddy_linux_amd64_custom
sudo dpkg-divert --divert /usr/bin/caddy.default --rename /usr/bin/caddy
sudo mv ./caddy_linux_amd64_custom /usr/bin/caddy.custom
sudo update-alternatives --install /usr/bin/caddy caddy /usr/bin/caddy.default 10
sudo update-alternatives --install /usr/bin/caddy caddy /usr/bin/caddy.custom 50

If Caddy is already running you'll probably want to restart it using sudo systemctl restart caddy.

When a new version of Caddy comes out it won't update the binary (because it has been diverted), so to update it manually you'll need to redo a few of the steps:

Download (and transfer if necessary) a new binary, then from a terminal:

chmod +x caddy_linux_amd64_custom
sudo chown root:root caddy_linux_amd64_custom
sudo mv ./caddy_linux_amd64_custom /usr/bin/caddy.custom

(Plus again sudo systemctl restart caddy if it's already running)

Typing all this out makes me so glad Watchtower exists for my Docker containers. I just made a Github Action to do a daily rebuild of Caddy with my modules, put that image name in my docker-compose.yaml, and Watchtower takes care of the rest.