Is this Computer upgradable? If so, help me build it!

Well in 2010 I bought an Intel Inspiron 580 (i3 with 6GB RAM). I wanted to upgrade this computer and I will replace the PSU and put in a Sapphire 7870 XT. So should I just get a new motherboard or will mine do fine? I have a budget of $500 - 7870, A case and 600w PSU. I am keeping the RAM so what should I add within that price point.

If you have $500 sell the pc off and use that extra cash and build a gaming monster (just my opinion)

I agree with cooper. If you can sell the pc for 200-300$you could have a pretty sweet build.