for information about changing your synology raid setup you should consult synology documentation related to your device, however there are a great many people in here using synology so if you wait a while i’m sure somebody will be able to take you through it step by step, if needed…
usually adding, removing harddisks and changing between raid 0, raid 5 and raid 6 is possible on
i would think synology supports that in most aspects, you shouldn’t have to delete or clear out the system or even shut it down to convert the raid, depending on what you are trying to do ofc.
you should always take backup of things that is backup worthy before doing major configuration changes to something like a raid array… you should always have backup of your important stuff obvious… following the 1.2.3 concept
in regard to the storagenode… taking backup’s of storagenodes isn’t realistic, you can copy a storagenode, just remember it has to be offline for the last sync… so that all data in the copy is 100% the same when you switch from the old to the new
information regarding node migration can be found here.
this is the go to guide for most stuff related to basic storagenode operations.
synology raid related information, ofc you might need to find the right one for your product…