Den12172,   From what I see there isn't a supported way of doing it, short of backing up the data, then deleting and recreating the Virtual Disk with the newer drives, and restoring the data from backup.  There are other non supported options like replacing each drive, one at a time and allowing it to rebuild, but that doesn't extend the virtual disk nor does it have the stability that recreating would provide.   Let me know if this helps.      
One of our customers has a VRTX with shared PERC8 and 25x 2,5" bays. He now wants to change the 600GB 10k SAS drives to 1,2TB ones. How can this be done? We couldn't find "replace member" as option like on normal PERC cards. The documentation says online capacity expansion is not supported, so what would be the "offline" way? Shutting down the server is possible. Delete and recreate the volume ist our least favourite option.
PowerEdge VRTX Capacity Expansion