Follow the instructions below to change the default port:
1) Login to your Linux server with root user through SSH. It is always good to have backup of the file before you make any changes to configuration files so without fail create backup of ssh config file /etc/ssh/sshd_config
cp /etc/ssh/sshd_config /etc/ssh/sshd_config_backup
2) Open the file with any text editor. I have used vim editor.
It will contain the line as Port 22 as mentioned in below image:
If the line is commented with character # then first remove that character so that server can identify to execute it. Now, mention your desired port as Port 2121(you can use other random port ranging between 1024-65535)
3) Save the file & restart the sshd service
4) service sshd restart
Generally, it is recommended to reboot your Linux VPS after changing the default port.
on next ssh access, you will require to use the port like ssh firstname.lastname@example.org:2121
[Note :- you must open that randomly set port on your firewall]