Items can be unlinked from the unit by using the Create / Link form. Right click on the item and select Create / Link > …
In the Create / Link form you will see all the linked items on the right side of the screen. Use the red arrow next to the item, to move it to the left side of the screen.
When you unlink an item, a window will open to show you a preview of all the linked items that will also be removed, you will click on Yes if you would like to proceed.
For more information on the Create / Link form click here and the Remove Preview, click here.