To change a user's password, you must be a Super Admin in the LUNA system.
Start by selection the Users tab at the top. Next, highlight the user who's password you want to change and click on Edit Selected button.
A new Edit User box will open where you can type a new password into the Password box. Then re-type the same password into the Confirm Password box. When finished, click the Save button to save the new password to the system.
Logout of LUNA (located in the top left toolbar) and then log back in with your username and new password.