So I probably did this wrong, but as the title states, I replaced the 2TB x 2 WD Red drives with 4TB x 2 WD Red drives. I removed one drive at a time and had it rebuild the raid. I am running RAID 1. I have a feeling it partitioned the new drives to match the 2TB drive thus the no increase in available space. If this is the case, how can I reformat the 4TB to make them a 4TB drive again and then copy the content to the 4TB drive without losing the added space?
As you have rebuild from the same RAID which placed the same RAID configurations of 2x2TB drives in 2x4TB drives.
In order to get complete 4TB storage from 2x4TB Red drives in RAID 1 configuration, you need to configure drives with new RAID 1 configuration. Note: It is recommended to store your important data in at least two locations.