Upgrade the Hardware of a NC Installation

I have a NC installation on a Raspberry Pi 3 with an external USB 2.0 HDD 1 TB:

Raspbian 4.19.66-v7+
PHP 7.3.9
nginx 1.10.3

Now I 've purchased a Raspberry Pi 4 with an external USB 3.0 HDD 1 TB. What is the easiest way to migrate the existing NC installation into the new hardware? The HDD is mounted in /var/www.