Please note that the photo can be misleading: it doesn’t depict the grounding contact (see passages above and below) that at this point should still be in place.
I found it’s much easier to skip this step, remove the three screws and lift the fan: this way the connector pops out with no effort and no risk.
I second what Trevor wrote: it's actually pretty easy to work around the cable without unplugging the connector and, as it's extremely delicate, I therefore recommend skipping this step.
Installed 8GB of RAM without problems. :)
Been wondering if this system would support 16GB though, given that appropriate modules seem to be on the market, that it has a 64 bit EFI and that the never versions of OS X, booted in the 64 bit kernel (which has been the default mode for a few years, now) obviously support that and more…