The HD4000 can be disabled but not 'upgraded' since its built into the processor. Installing an aftermarket GPU usually disabled the iGPU (hd4000) but sometimes you have to boot into the bios with the iGPU and then set the boot graphics card to pcie or PEG and then shutdown and install the new GPU and boot back up.
Correct by the way I wish there was a HD40k like your title suggests only jesting
Pop is correct you would more then likely need to change out your power supply there are a few things manufactures go cheap on in store bought computers. It's hard to say what your bios would want you to do. There was a lady on the forums I was helping where she had to install the card drivers disable the onboard card in device manager and then switch the adapter to the graphics card pci in your case pci-e and then it would boot fine.