Synology NAS DS216+II 8TB SHR with data protection to non data protection without losing data

I have an 8TB Synology NAS in SHR with data protection, which is about to be full.

As data protection takes up 4TB, I would like to make use of it as a normal drive. As I have my data backed up elsewhere I don’t need this protection disk anymore.

Any idea how to transform SHR with a protection disk to without a protection disk, to get extra space, without losing any of my data?