Yes, e.g. with an already existing EX2 you can exchange the disks for those with a larger capacity, if you operate them in RAID mode, both must have the same capacity.
It says at the top, directly under the picture, that this product is available with the following configurations:
"2x2TB, 2x8TB, 2x6TB, 2x4TB" If you click on the corresponding buttons, the price will even be displayed.