1. Login to your centos system with root or user have sudo.

2. cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

3. vi /etc/ssh/sshd_config

Change "Port 22" to "Port 42"

save the file.

4. use "systemctl reload sshd" to load the new config.

5. open another terminal to ssh vps, if failed, restore sshd_config and reload service.

Or you can use tools follow github:

https://github.com/AutoAndEasy/sysinit

I want double ram for free ~ thanks ~