Replacing ex2ultra with ex4100 - how to migrate files?

As the title suggests I’m upgrading my nas and want to migrate files. What’s the easiest way to do that? Can I connect both devices via USB ? Or can I connect the ex2 ultra to the extra Ethernet port on the ex4100?

You can not connect one device to another via USB or Ethernet.

The most reliable method is a direct file transfer (Cpy & paste) across your network after both NAS devices are mapped.