You should always use a secure channel for password operations but this requirement can be disabled for testing purposes using dsmgmt.exe:
C:\Windows\system32>dsmgmt
dsmgmt: ds behavior
AD DS/LDS behavior: connections
server connections: connect to server localhost:50001
Binding to localhost:50001 ...
Connected to localhost:50001 using credentials of locally logged on user.
server connections: quit
AD DS/LDS behavior: allow passwd op on unsecured connection
Successfully modified DS Behavior to reset password over unsecured network.
AD DS/LDS behavior: list current ds-behavior
Password operations on unsecured connection: Allowed.
AD DS/LDS behavior: quit
dsmgmt: quit