If you are within Windows, install the RAID controller software from the HP disks that came with the server. If not you can reboot and go into the RAID controller BIOS and break the array from there.
However if you break the array you should expect that you will loose all data on the array.
Just realize within Windows you may break it since you are within the OS and on the hard drive containing it. Best way would be to reboot your system, press F8 or F9 when the section “HP Controller xxxx ” initializing and 0 raid founds.