First select attributes (or operations) whose visibility you want to change. If you want to select multiple fields, hold the CTRL key and click on a field (attributes, operations). If you want to select all fields between last selected field and the clicked one, hold the SHIFT key.
The visibility can be changed these ways:
- using the context menu (right click on the selected field): Visibility/Private, Protected, Package, Public
- using the ribbon: Field/Modifiers/Visibility/Private, Protected, Package, Public