Enforcing Password history
Enforcing password history will define how frequently the passwords can be used from the history base. These settings can be administered using the Security Enhanced Directory Manager plugin
Here are the steps
Go to System Settings>Directory Manager Settings>Configure Plugin(Security Enhanced Directory Manager)>Default Directory Password Policy
The default is set to 5 for "Number of Unique Passwords Before Re-use". A select box allows an admin to select other options or remove this setting from the system.