How to delete RAID array with CTRL + i
Turn on the computer. When prompted during system startup, press Ctrl + i to enter the option ROM user interface. Use the up or down arrow keys to select “Delete RAID” Volume. Use the up or down arrow keys to select the RAID volume. Press Delete to delete the volume. Press Y to confirm the deletion.
How to delete RAID array with Intel Rapid Storage Technology GUI (and Intel RSTe as well)
Open Intel Rapid Storage Technology enterprise tool within Windows* Click home button and select the array  Under Volume properties, at the right side, you should be able to see "Delete volume" Click it and then select yes
Once the volume has been deleted, it should be possible to see involved drives as individual drives.