Default wipe cache partition

OK so I have been searching all over the internet and I haven't found an EXACT answer on how to do this. I am TRYING to wipe cache partition on my LG Optimus G Pro, reason being is I cannot download 4.4.2 even after doing a full unroot via SuperSU. It still says my phone is suspected in rooting and cannot download update. I read on one site that doing a wipe cache partition may allow the update. When I try volume down + power, I get a screen that says 'factory data reset, press power key to confirm, any other key will cancel'. When I press volume up + power, it boots into safe mode. So I am quite frustrated by now. Any help would be great, thanks!