Expand Raid-5 Array

Hello

I have a HighPoint RocketRAID 454 for both Windows XP SP2 and 2000 SP4(+Rollup).

One array is RAID-5 with 3 disks and I would like to add another disk to this array.

I know I can add a new disk if the array is broken but how would I “expand” an existing (working) array without data loss?

Thank you.

Regards,

seb