To delegate the right right to unlock user accounts in ADUC:
Right-click the OU or domain in Active Directory Users and Computers and select Delegate Control from the context menu
Click Next on the Welcome dialog
Click Add to select the user or group and click OK
Click Next
Select Create a custom task to delegate and click Next
Select Only the following objects in the folder. In the list, check User objects and click Next
Clear the General checkbox and check the Property-specific box
Check both the Read lockoutTime and Write lockoutTime boxes and press Next
Click Finish