Just to be sure on the configuration you are using, how many hard drives are installed in the system?
Are you using 4 hard drives, and each RAID volume in pairs? If this is the current configuration, you should be able to do this just settings the desired volume to non RAID and following the information on this article:
Intel(R) Rapid Storage Technology (Intel(R) RST) | Move a RAID 1 volume to larger hard drive
If you are using 2 drives, using what is called Matrix RAID configuration, then this would not be possible. You would need to back up and create a new RAID one with the new drives.