Need Advice about Power supply and Overclocking

i've got: i5 3470 3.2Ghz,P8 H61-MLX3 Plus 2.0 Motherboard,Asus Nvidia GTX 650 1GB,4GB ram,500GB HDD.Windows 7 Ultimate 64-bit.
i don't know how much Power Supply my pc have got maybe 450W and i'd like how much is enough for gaming.
I'd like to overclock my PC a bit if it is possible.Thanks !

You CPU doesn't overclock to start with and that GPU isn't too demanding. What is the name and rating of your current PSU. If it's a decent make then you really won't need to upgrade it.