How old is the Antec PSU and what is the exact model? 550 is the wattage, it doesn't state the model. You will also need to state the budget you have allocated for said upgrade, regardless of what part to buy.
List your current specs like so;
Also, can you check and see which BIOS version you're on for your motherboard at the time of writing? You should be able to overclock the rams but that's only if the airflow in your case is good to deal with heat dump and your IMC being taxed.