Before uninstalling you can take a backup as suggested https://help.qlik.com/en-US/sense/3.0/Subsystems/PlanningQlikSenseDeployments/Content/Server/Server-Backup-Restore.htm
I hope this is helpful.
Coincidentally we're actually going through the basically the same thing. We're moving from a single node 2.1.1 to multi-node 3.1. The backup and restore does require the files to be restored to the same server.
We're using AWS and our solution was to take a snapshot (AMI) of the server and use that image to instantiate the new server. You'll have to work through certificate issues at first, but this is the most thorough and quickest way to do replicate an environment.
Later on down the road we found our image to not be as stable so we had to start from scratch Hope your luck is better!
I think taking snapshot backup of server would not work int his case.
You can do a repository database backup & restore on different server.
We have moved from multi node to single node. The single node was on new physical server where we have restored the backup taken from old central node of multi node.
You can also restore certificates.
Follow below URL for taking backup
Follow below URL to restore the backup
Hope this is helpful.