Product key change error MS CRM 2011

Hi there,

I want to change product key for my MS CRM 2011 installation but I'm getting below error

Error Message

The product key is not compatible with the installed version of Microsoft Dynamics CRM. Make sure that you have typed the correct product key, and then try again.

Later I came to know I've installed Microsoft Dynamics CRM Server 2011, but I've Microsoft Dynamics CRM Workgroup Server 2011 product key.

So, is any way to convert Microsoft Dynamics CRM Server 2011 to Microsoft Dynamics CRM Workgroup Server 2011

How I make this work ?

Thanks,

Kiran.