So, you have 4 disks in a TWO different RAID 5 VD's across those 4 disks? If that is the case, you are stuck with it unless you do a backup/restore and delete and reconfigure the array(s). "Slicing" the disks with different arrays nullifies any expansion option. Even if you could do a "Reconfigure" with slicing, you would be expanding BOTH VD's in the disk group - you couldn't add the space to just one of the slices. I'm also not sure if you can even do this from the BIOS of an H310; you could with an H700 and above with a minimum firmware, but I'm not sure the lower-end H310 got that option or not. If not, you would need to use OMSA. As an alternative to a full reconfigure/backup/restore. You should be able to backup your data VD, then "Reconfigure" the VD to expand to fill the disks, THEN either expand by adding disks or create a new VD with the new disks. Of course, if it was sliced in the first place because of the 2TB boot disk limit (not using UEFI), then you need to rethink the whole scenario. What size are your disks? 
I have a PowerEdge T320 with a PERC H310 installed.  Currently, it has 4 physical drives with two virtual disks.  Both are RAID-5.  One for the OS, the other for data.  I have installed 4 new physical drives into the server that I want to add to the "data" virtual disk.  The drives are showing as Ready within OpenManage, but it's my understanding that there should be a Reconfigure option on the virtual disks.  I do not have that as an option.  I was hoping I could expand this virtual disk while the server is online but now wonder if I can expand it at all.  I have not scheduled an outage yet to try booting into the BIOS to reconfigure.  Wanted to see if there was something I was missing or something about my configuration/version that does not allow me to reconfigure the virtual disks.
PERC H310 adding drives