If you change the ticket at "ANY TIME" then there will be a $75 fee - however that doesn't mean that it will only cost you $75 to make the change.
In addition to the change fee, most airlines will also charge you for the "fare difference" for your new flights. The fare difference is the difference between the price you paid for the original dates, and the equivalent price for the new dates that you're booking. It's possible that the fares for both dates will be the same, but (for example) if the new dates you're looking at traveling are in a busier time period then it's likely that they will be higher than your original fare. In that case you'll have to pay both the difference in fare between those two dates, PLUS the $75 change fee.
If the new fares turn out to be cheaper, some airlines will give you a refund (minus the $75 change fee), whilst others will not.
The "ANY TIME" in the rules refers to the fact that you can make a change at any time - even after the first leg of your journey has started. eg, you can change the time of your return flight even after you've completed the outbound flight. Although it's not stated in the snippet you've quoted you probably need to make the change before the flight you're booked on departs. (eg, if you miss your flight, then likely you can't just ask them to move you to a flight the next day). Often you'll see this specifically listed in the fare rules as something like 'NO VALUE AFTER DEPARTURE" or words to that effect.
The "BEFORE DEPARTURE" in the cancellation section means that you can only cancel the ticket (with a corresponding $150 fee) before any of the legs of the flight have been flown. eg, you can't take the first leg, and then cancel your return (or at least, you can, but you won't be getting a refund!)