It might be pretty difficult to drop disks from a volume of that size, especially since you're using RAID 10.

With a RAID 5/6, you can fail one disk at a time and shrink the array in small blocks. With RAID 10, you would have to shrink the filesystem enough to remove one of the mirror sets. Then fail those disks out of the RAID and recreate the array with fewer disks. I'm not sure that last step will work, because if you failed two disks from the same stripe out of the array, the whole volume would be in a failed state (unlike RAID 5/6 which would just be degraded).

Since you don't seem to have too much actual used storage, it would probably be a lot easier to copy the data to another volume and rebuild the array with the reduced number of disks you want to use.