Your GPU is the weakest part. Easiest upgrade is to get 750 TI.
R9 270-270x or GTX 960 are better but you will need an PSU upgrade also. Upgrading the CPU to six-octa core will also increase performance but best performance boost will be from video upgrade.
ATX 350 Power Supply. How do i know what i can upgrade to in terms of the type of power supply and gpu/cpu upgrades?
Also what makes the gtx 750 ti better then mine? GDDR5?