The processor is fine, its still enough to play games.
No point upgrading the mobo.
RAM can do with an upgrade. See if you can find another of the kit you already have. If not, 8GB of 1600Mhz CL9 will do just fine.
PSU is fine, though should start thinking about replacing it in a year or so as it is getting a bit old and PSU's do degrade over time.
Which GPU you could get depends on the amount of cash you have to upgrade.
~$300: GTX660Ti or HD7950 depending on games you play.
~$450: HD7970 Ghz
Money grows on tree's where I live: GTX690.