Your GTX660 and 4gb is below recommended specs.
The I5-3470 is ok.
Here are the specs and some suggestions for improving:
https://www.killping.com/blog/ways-to-workaround-fortnite-lag/
Think carefully about how you upgrade ram.
Ram is sold in kits for a reason.
A motherboard must manage all the ram using the same specs of voltage, cas and speed.
The internal workings are designed for the capacity of the kit.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards can be very sensitive to this.
If your motherboard has 4 ram slots, I suggest buying a 2 x 4gb kit with the same specs as your current ram.
You know you will have 8gb that works.
Then try adding in your old...