What storage controller you have on the server? Is the new disks which you want to replace is same type and family of current disks? If you have same type drives then you can replace drive by drive. For this you need to make one drive offline, replace the drive and wait till the rebuild to complete. Once rebuild is complete you can repeat the same with second drive. If rebuild did not started automatically after replacing the drive you can assign the drive as hot spare for rebuild to start. You can refer below link for details

https://www.dell.com/support/kbdoc/en-us/000143539/poweredge-hdd-how-to-physically-replace-an-hdd-hot-swap-procedure?dgc=SM&cid=243909&lid=spr6153914739&RefID=dtw22_sm6153914739&linkId=146721776 

To replace a physical disk in a virtual disk you need to have same type (HDD or SSD) and family (SATA/SAS)  drives. Size can be same or more. Can you share details on the current drive and new drives which you are going to replace.