Place your cursor over Reference Data and left click on the sub-option Incident Size Classes.
Find the incident size class that you would like to edit and left click on the Edit button 
on that line.
Enter the changes that you would like to make to the information.
Use your Tab key on your computer keyboard to navigate through the fields or left click on each individual field.
Left click on the Update button 
to save the edited information.
Left click on the Cancel button 
if you do not wish to save.