How to change web.config without loosing session

In application  by default we have InProc session state and due to this our session is stored in application memory that's why when we change web.config, it lost session also.

sessionState mode="InProc" timeout="30"

To overcome this  problem use "StateServer" session state. It stores application session in server memory where our application is hosted.

sessionState mode="StateServer" stateConnectionString="tcpip=127.0.0.1:42424" timeout="30"

Thanks
Anil