1 - back up your data
2 - power the unit off
3 - remove a drive - pick one, any one
4 - power the unit on
5 - login to the web interface
6 - select Tools/RAID/Set RAID Type & Reformat.
7 - wait for the format to complete & reboot
8 - power the unit off
9 - replace the drive removed in step 2
10 - power the unit on
That wasn't so hard was it?