In version 6.1 & 6.2 the menu Physics>Material Table brings up a small dialog box with options to Modify, Create, Delete, Assign or Inquire Materials. The Modify and Create options open up a Material Editor dialog box where you can choose the material property you wish to modify and (if they are characterized by a single number) type in a new value. A nonlinear material or a permanent magnet is characterized by more numbers and requires either clicking to edit the data in AutoGraph or loading a new material. See the video Loading a Nonlinear Magnetic Material.
When using AutoGraph to edit a material remember to click Apply in the Material Editor before closing Autograph. Many customers prefer to open an existing material file and use it as a template. They change the name, paste data in from a spreadsheet, and save under a new name to be loaded as shown in the video.