Step 1

As root, use your favorite text editor (vi) to edit the sshd configuration file.
vi /etc/ssh/sshd_config

Step 2

Edit the line which states ‘Port 22’. But before doing so, you’ll want to read the note below. Choose an appropriate port, also making sure it not currently used on the system.

# What ports, IPs and protocols we listen for
Port 50683

Step 3

Switch over to the new port by restarting SSH.
/etc/init.d/ssh restart

Step 4

Verify SSH is listening on the new port by connecting to it. Note how the port number now needs to be declared.
ssh username@hostname.com -p 50683

 
Fuente: http://linuxlookup.com/howto/change_default_ssh_port