You will lose everything on both discs. Everything.
Make sure you have the correct RAID drivers for your controller on Floppy.
If you have XP, you will need to have them, or XP will not be able to see the array. If you have Vista, you should not need them, but never the less, put them on a floppy now, before you do anything else.
Simply enter the RAID BIOS, (look for the message during POST)
Break the array, rebuild the 2 disks into a striped set, or RAID 0.
This also will basically wipe everything off both drives.
Reboot, and prepare to reinstall your OS.
jitpublisher is both correct and incorrect about converting to RAID 0. The first question has to be, what do you expect of RAID 0 over the RAID 1 setup you currently have? You will lose all fail-over capability you currently have, and the very slight load/run speedup you think you're getting maybe milliseconds versus the time frame you're hoping for. Backup your current system with ACRONIS, to an external drive, or maybe a third installed drive. Run the BIOS routine to set the drives for RAID 0 and initialize. Boot the computer with the ACRONIS CD and select to restore the image to the RAID 0 disks. Have the drive controller drivers on a thumb drive and point the ACRONIS software to inject them while doing the restore. Your computer will then be the same as it was, just changed to RAID 0...