WD NAS Upgrade

The EX4 (24Tb, 512Mb, RAID5) has reached the end of its life, the box has simply run out of capacity,
So after careful consideration, I bit the bullet and have upgraded to a PR4100 (32Tb, 16Gb, RAID5)
What is the quickest way to copy all the existing files from the EX4 NAS to the PR4100 NAS. please ?

Remote backup from EX4 to PR4100 would work as long as the EX4 has enough cpu/memory to process the data.

Thanks All, The file transfer went very smoothly,
I connected the EX4, the PR4100 and a Dell I7 PC to a dedicated 8 port Netgear Gigbit switch,
The switch was then connected directly to the 2nd port of our modem/router.
(The 1st port has a 16 port Dell Switch plugged into it, and a large number of other devices plugged into that switch, requiring Internet Access).
Logging in as ADMIN, I mapped the Y: for the EX4 and the W: for the PR4100
Concerned now with the time taken to constantly update the screen while using some file transfer programs.
I used a free version of Total Commander, and simply set the file transfer as a background task.
Everything is up and running, and the performance improvement is just out of this world.
Thanks again