How do I update URBackup on an Open Media Vault server?

Server
4

What is your architecture
RPI ?
X86_64 ?

You download the good deb files.
I think it is UrBackup Server 2.4.11 Debian/Ubuntu stretch(with backports)+/19.04+ amd64

and install it on you system whith ssh
dpkg -i urbackup-server_2.4.11_amd64.deb