Occurrences are designed to manage details in across a group - the option to change enrolled unit fields allows you to have more control over details that may differ from unit to unit, or enrolment to enrolment within your Occurrence.
This specifically allows you to update the unit hours, delivery modes, release number, or reportability for that unit in selected enrolments in the occurrence in bulk.
To access this option, Expand the Units/Modules Heading and Right-click on a Unit:
This will display the Change Occurrence Enrolled Units Wizard: 
- Select the Field to Change, including the unit hours, delivery modes, release number, or reportability for that unit.
- Select the new value for the chosen field. This will be applied upon finishing the wizard.
- Select the applicable Student Enrolments in the particular unit.
Press Next to progress the wizard.
If you require for this change to be applied to the Occurrence itself, you can tick the Make the same change to the occurrence unit (to apply to future enrolmnets) option.
Press Finish to complete the process.