Hi anil,It will be updated at the next fsimage checkpoint.
There are other methods of update :
1-execute this command in the secondary namenode or the standby one
dfsadmin -saveNamespace
2-or by changing the parameters :
dfs.namenode.checkpoint.period,
dfs.namenode.checkpoint.txn,and the period of checking these conditions:
dfs.namenode.checkpoint.
Note: this operation is CPU and memory intensive you should choose the right time and parameters.