I am running a server with version 1.3.16 and I never upgraded since this version. Although I have snapshots of the server and both local and remote daily backups of the hosted websites, I was wondering if it would be considered safe to directly upgrade to the latest stable version (currently 1.5.1)?
My server is on a Debian 8 distro.
I also have installed the Let's encrypt plugin on this server and I already use it for the admin panel and the hosted websites.
Can someone briefly provide some info on how to safely upgrade my server with the minimum service interruption?