Upgrading my computer?

i have a intel graphic card so am wondering if i can upgrade it to a geforce or can i only upgrade it only with in the intel cards.also i want to know how can i tell if a psu will fit in my computer just by a pic of it and am also wondering if there is any requirements for upgrading the Processor to a AMD Athlon II X2 255 and if there are requirements to upgrade to windows 7 home premium