Update upgrade docs

doc/manual/source/installation/upgrading.md

@@ -1,34 +1,10 @@
 # Upgrading Nix
 
-> **Note**
->
-> These upgrade instructions apply where Nix was installed following the [installation instructions in this manual](./index.md).
-
-Check which Nix version will be installed, for example from one of the [release channels](http://channels.nixos.org/) such as `nixpkgs-unstable`:
-
-```console
-$ nix-shell -p nix -I nixpkgs=channel:nixpkgs-unstable --run "nix --version"
-nix (Nix) 2.18.1
-```
-
-> **Warning**
->
-> Writing to the [local store](@docroot@/store/types/local-store.md) with a newer version of Nix, for example by building derivations with [`nix-build`](@docroot@/command-ref/nix-build.md) or [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md), may change the database schema!
-> Reverting to an older version of Nix may therefore require purging the store database before it can be used.
-
-## Linux multi-user
+You can upgrade Determinate Nix using Determinate Nixd:
 
 ```console
-$ sudo su
-# nix-env --install --file '<nixpkgs>' --attr nix cacert -I nixpkgs=channel:nixpkgs-unstable
-# systemctl daemon-reload
-# systemctl restart nix-daemon
+sudo determinate-nixd upgrade
 ```
 
-## macOS multi-user
+Note that the `sudo` is necessary here and upgrading fails without it.
 
-```console
-$ sudo nix-env --install --file '<nixpkgs>' --attr nix cacert -I nixpkgs=channel:nixpkgs-unstable
-$ sudo launchctl remove org.nixos.nix-daemon
-$ sudo launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist
-```