I do agreed sorry but one can't
The E521 is different from ATX form factor cases, motherboards and PSU, one can't upgrade this computer because it is BTX form factor. The BTX design is design defferently the ATX is much smaller one would not be able to fit the PSU into a ATX case and one won't be able to screw the motherboard into the chases. That's Dell !!! always looking for one best interest.