Thanks JorgeB,
Just to make sure, follow this procedure?
Stop the array
Unassign the old drive if still assigned (to unassign, set it to No Device)
Power down
Pull the old drive
Install the new drive
Power on
Assign the new drive in the slot of the old drive
Go to the Main -> Array Operation section
Put a check in the Yes, I'm sure checkbox (next to the information indicating the drive will be rebuilt), and click the Start button
The rebuild will begin, with hefty disk activity on all drives, lots of writes on the new drive and lots of reads on all other drives
All of the contents of the old drive will be copied onto the new drive, making it an exact replacement, except possibly with more capacity than the old drive.
Thanks again.