According to Apple's Configurator 2 documentation, you can remove the Supervised status of a device, but doing so erases all content and settings, including apps and media. Therefore, if you want to preserve the data on the device, you should make a backup of it first. Note that a backup of a supervised device can be restored only to another supervised device.
To remove supervision from a device, open Configurator 2, select the device, and then select Actions > Advanced > Erase all content and settings. This will remove the supervision and reset the device to the default factory settings.