I know this is an unusual request but is better to be prepared with this quick and easy guide.
In the case that you need to get more VMs running on your Windows Server 2012 Standard server (which is limited to two virtual instances), you can just get DataCenter Product Key and convert your current version without the need of installing the OS from scratch.
First of all, we need to open an elevated command prompt and determine the current edition we are running, this can be done by typing the following command:
DISM /online /Get-CurrentEdition
Our Current Edition is: ServerStandard
In order to proceed with the conversion we need to make note of the edition ID we want to convert, Data Center uses the ID ServerDataCenter, this will be run with the following command:
DISM /online /Set-Edition:<edition ID> /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
You will need to change the edition ID and the product key you acquired.
And finally, Press Y and will cause the server to restart twice. When you log back again, you will be now running Datacenter
That’s pretty much it, hope you find this guide helpful,