To play on the Private Server you first of all need to download the client.
HERE
Or you can use the online client [may not be as stable]
HERE
Once you have fully downloaded the file, Extract it to some where of your choice and then go into "Highscape Client" folder and double click "Run.Bat"
This will load the client, Give it time and it the main menu will load. Click enter and enter a Username / Password
DO NOT USE YOUR DHGAMING PASSWORD
Enter the username and password you would like to use, And this will create your account.
Server IP : dhgaming.no-ip.biz [Should be default]
Port: 43594 [Should be default]
You will then be logged into the server!
Enjoy!