Hi Valliappan,
Check liveupdate policy, according to liveupdate policy SEPM will update himself.
Screenshot is attached for reference.
Ideally once SEPM updated it will pass on those updates to clients, however check following settings.
Check your SEPM is in push mode or pull mode
Push mode
The client establishes a constant HTTP connection to the server. Whenever a change occurs with the server status, it notifies the client immediately.
Pull mode
The client connects to the server periodically, depending on the frequency of the heartbeat setting. The client checks the status of the server when it connects.
I hope it will help you !!!