Changing courses includes course transfers, as well as changing majors/minors and specialisations.
You should seek academic advice before applying for a change or transfer as you can only submit one application per session.
Change of unit is for students who wish to make changes to the units in their study program, eg enrol or withdraw.
A concurrent degree is a second undergraduate degree that you start while you're still studying for your first.
Concurrent unit studies are for students enrolled in a bachelor degree program at Macquarie University who would like to undertake unit(s) at another Australian university to count towards their Macquarie degree.