My first pc build

Depends on where you are looking to improve.
If you are running a lot of CPU heavy games then something like an FX6300 or FX8320 might give you a nice boost.
Unless you are monitor limited (ie a small resolution) then it's most likely you'll see a bigger gain from upgrading your graphics card. The 650Ti is pretty solid lower-mid range, so there's not a huge amount of sense in replacing it with something unless it's a good step up, say a GTX760 or something in that area.