Technically it should support up to the highest end iCore (a i7). The problem is that would no longer make this a "hewlett packard (model) 500-281" but a different model computer which would potentially violate your Windows license. The Windows license is TIED to the hardware, which means you can't modify the motherboard, cpu and sometimes not even replace the case itself (EMachines did this to me) without Windows ceasing working immediately when it starts up because it detects the difference so it know 'how to talk right to the hardware'.
Secondly to that, changing CPUs only helps if you need more 'processing', so if you multitask ALOT, with normally 30 windows open in Chrome, streaming both a video and music in two different...