ALTREMOTE_UPDATE vs PFL megafunctions

I think I have read too much about Remote Update to completely confuse me.

I have a Cyclone IV FPGA that I want to remotely update. I need to find out which Megafunction should I use.

Basically if someone can tell me the when the ALTREMOTE_UPDATE Megafunction is used versus when the PFL (Parallel Flash Loader) Megafunction is used for remote update.

Cheers. :)