On any Intel(R) Desktop Board with RAID support you should be able to delete the volume with no limitation on the Intel(R) Matrix Storage Manager option ROM using the Control+I key stroke method. An option to set the hard drives to a non RAID configuration or an option to delete the RAID 1 array should be available.
However you are using a DELL system, in which the option ROM may be implemented and accessed in other way and the options available would be different. You should check this directly with your Original Equipment Manufacturer.
What is your "IDE configuration" set to in BIOS? If your seeing the RAID utility when pressing "Ctrl + I" while booting then it is set to "RAID" in BIOS. If you change the setting in BIOS "IDE configuration" to "IDE" it should show the drives separately. However, if the OS was installed with the "IDE configuration" in BIOS set to "RAID" it may cause problems/not work, if that is the case set the "IDE configuration" back to "RAID"
Pulling a disk will degrade the volume but will not remove it. If you enter the option rom (by hitting ctrl+I) during boot, then reset ONLY one of the disks, it should have preserved the data and partition table on the disk you reset. Then simply remove the other disk from the system and try to boot from the disk u reset. If the new non raid disk doesn't boot then u can always re-add it to the raid one volume again. However the disk that u reset should be fine. Changing it to IDE mode will NOT work. The drive and os configuration was installed in RAID mode... Changing it to IDE will prevent u from booting