Hi,
If you are planning on keeping the RAID Array but want to erase the data on it then you shouldn't need to change any settings. If you are planning or have your OS on this Array, you will, of course, have to go through the original process of pre-loading drivers when you reinstall but you will not need to make any changes in BIOS.
If you are planning to change from a RAID Array and use your HDD's as single units then yes, it would be better to change the settings in BIOS to either IDE or AHCI.
ATB