Here I will show you how to change port from 2222 to 9999 in two steps.

Step One: DirectAdmin

To change port of my choice (e.g., 9999), I have to open directadmin.conf as follows

vi /usr/local/directadmin/conf/directadmin.conf

Change port from 2222 to 9999

port=9999

Save and exit vi

:wq

Step Two: CSF

Find and change ports in CSF (ConfigServer Security & Firewall). Open csf.conf

vi /etc/csf/csf.conf

Change as follows:

TCP_IN = "9999"
TCP_OUT = "9999"

Save and exit vi

:wq

Restart the CSF firewall

csf -r

Then restart the DirectAdmin

service directadmin restart

You can do above task in login to DirectAdmin too.