Which Design pattern i should use - Server should handle multiple request types

I have an application, which has windows service and a user mode application. The windows service acts as a server and user mode application acts as client. Client can send requests and server will perform the operations. I am planning send data in JSON format.

Also I am planning to use named pipe to communicated between the service and user mode application. I created a POC to test this, every thing is working fine.

My question is, in server how to handle the multiple request type.

1) Which design pattern i should use.

2) Currently i am using JSON, later i may use XML or some other format.

3) Later this design should be able to add new request with out any much changes in communication layer.

4) Client sends different request types like, Update Employ data, Update system info, remove unused Clients data and etc