It is not possible to do this.  The PERC's support Online Capacity Expansion (OCE) and RAID Level Migration (RLM), but OCE works only by ADDING physical disks, and RLM cannot migrate an array to a smaller array/size.  You will need to backup, delete VD (7-disk), create smaller VD (6-disk), restore.
Hi we have a Raid-5 set contains 7 Hard disks in Dell R710 server. One hard disk space contains 300 GB. The Raid5 set contains enough free space. I want to remove one hard disk from this Raid-5 set. is it recommented to do this? i hope once we remove the hard disk Raid set will reconstruct with 6 hard disk if they have enough space. Appreciate the comments.. Thanks Akther  
Need to remove Hard disk from existing Raid-5 set