Upgrading System Center to UR3, UR4 or R2

Hi,   Some general upgrade questions.

If we are at UR2 can we go to UR4 and this adds UR3 changes as well? or do I need to do each of them?

If we upgrade SCOM to UR4 do we or should we upgrade Service Manager, Config Manager, VMM, Orchestrations, App manager, etc all together or can we do them separately?

Lance

Thanks Lance