Update NEXTCLOUD on managed server. 16 -> 17 -> 18 -> 20

Job ID: 31453245

Budget: €30 – €250 EUR

I need a professional server manager for my Linux / CentOS servers. I have several instances of NEXTCLOUD software running. I need:
* security improvement
* version updates (from v. 16 stepwise up to v.20)
* on a live server (I need to having a maintenance mode visible)
* note: NO sudo functionality via ssh available
* TB's of data are hosted (no simple backup)
* max downtime possible: 24h !!!

Please apply with the solutions and your experience references ! Otherwise I may not answer you application. Please understand.
Related categories: System Admin Linux Apache Ubuntu Debian