I see two 80mm fan holes in the rear, only one of which has a fan deployed there.
I see a likely mounting spot for a front 80mm intake fan, in front of the lower drive cage.
Let me come clean with my bias -- I HATE 80mm fans when there is some way to use 92's or 120's. I have very good reasons to despise 80mm fans. Low throughput, high-noise at high rpms.
You could conceivably install an 80mm fan in that case in the front-panel position designed for it.
OR . . . remove the drive cage, remove the front facie/bezel, and examine how you might cut a bigger hole for a bigger fan and drill the four holes to mount it. Measure the distance from the plastic bezel/facie-plate to the metal chassis to see if a fan would fit between the bezel and the chassis, so you don't have to lose hard-drive space. Or see if there is a way to make a larger fan fit in front of that drive-cage -- mounted inside the chassis as is the prevailing and conventional way of doing it.
Without fear of damaging a new case I'd paid for, I would try by hook or by crook to find a way to get a 120mm fan in front. If not that, then a 92mm fan. If not that, you would just mount an 80mm fan as the case seems to provide for.
You can then decide whether you want to simply add the extra 80mm exhaust fan, or widen the holes to fit one or even two 92mm fans. (Again, if possible, I'd try and figure a way to put a 120mm fan for exhaust out the back side of the case, but this is not always possible.)
If there is any imbalance between CFM's going in and CFM's going out, you could ventilate the side panel, filter it, and duct it to the top of the CPU heatsink fan -- assuming that is your choice of cooling technologies. This, however, will increase noise. And mount an additional fan on the side panel will also increase noise, so I would try to avoid that over ducting the CPU fan intake from the side-panel.
With two fans of any size (or a single 120 if you could fit it) in the rear panel of the case, you can then use foam-art-board to build a duct over the motherboard and around the CPU fan, so that the CPU fan sucks air "in", and the duct -- fitted to the rear exhaust fans -- channels the air from the CPU heatsink fins immediately out the back of the case.