How can I use VS Code to update extensions via commandline?

I can't find a command to update my install extensions from the terminal.

Of course I use code --install-extension to install extensions. But how should I update them?

The --help docstring for --install-extension says:

--install-extension <ext-id | path> Installs or updates an extension. The argument is either an extension id or a path to a VSIX. The identifier of an extension is '${publisher}.${name}'. Use --force argument to update to latest version. To install a specific version provide @${version}. For example: vscode.csharp@1.2.3.

VS Code 1.86 and up also support updating all extensions via commandline, with code --update-extensions (see issue ticket #56578). If you don't pass a --profile argument, only extensions for the default profile are updated. If you pass a --profile argument, only extensions for that profile will be updated. Note that VS Code 1.94 added the ability to update extensions across all profiles (source), but I'm not sure if this is exposed in the CLI.