EX4 - Raid 5 and JBOD

Hello,
I bought my EX4 and 3 wd red’s at 3tb each. Had them working in raid 5 for a while when i managed to purchase another 3tb WD Red. I now have a Raid 5 with the original 3 drive, and a JBOD with the new one.
what i want to do is to have all 4 drives in the Raid 5.

How do i do this without losing all the information i have on the original raid 5.

I tried to expand the Raid 5, but it’s asking for the first drive to be removed and to have a new HDD added.
How do I Cancel that, and remove the JBOD, and then expand the original Raid 5?

Please help.
Thanks.

http://wdstagingsplit.staged-by-discourse.com/c/network-attached-storage/wd-my-cloud-ex4