Locate the item to remove
Click to expand the LaunchPad unit you would like to remove an item from (in this case, Chapter 3).
Click "More Options"
With your mouse, hover over the item you’d like to remove (Section 3b, in this case) and click the More Options button on the right.
When the prompt appears asking if you’re sure you’d like to remove the section, click the Remove button.
The item is removed
The section will no longer appear in the LaunchPad unit. However, you can always add any item you've removed back into the unit. It is never permanently deleted. See the help article Adding Removed Content Back into a LaunchPad Unit.