Enable remote desktop for more then 2 user

I run a small business, people access the server through local LAN via remote desktop. I am also running dyn service, to access the server via internet through remote desktop again.

The Remote desktop supports maximum 2 users at a time. How can i enable the option for more then 2 people to access the server?

If there is a step by step guide or instructions it will be very helpful.

Goal: Install Multi user Remote desktop on Single server

OS: Windows Server 2012 Standard