The only way to access these clips is through the ventilation holes, .. how convenient !

It's enough to unhook 1 clip per side, and one of the clips cannot be unhooked, as it's blocked by some black paper plastic rubber thingy

It is highly recommended you go in through the marked holes (those are the largest open areas inside the PSU anyway)

In case you have something thin and strong enough to do this without enlarging the holes: please leave a comment down below !

I drilled through the existing holes to make them large enough for a fittingly stiff screw driver

BEWARE : this plastic is incredibly brittle and will crack very easily; using a stepped drill bit for the plastic, then a regular bit for the metal worked best