Raid migration from Raid 0 to a Raid 1 can be possible only on a Server system with a Raid controller in it.
For a regular desktop system I would recommend you to create an Image of the RAID 0 into another disk.
Then, access the ctrl +I menu and delete the existing Raid 0 and create the new RAID 1 array.
Restore the image you backup on the new array
Remember that if a RAID 0 (striping) is currently giving you 2 x 500GB (1000GB) for example; a RAID 1 (mirroring) would only give you 500GB. So make sure the hard drives you are going to use to the RAID 1 have enough space when adding the data.
I suggest you to always back up all the information before making any change.