You can not expect a budget rig to not struggle a bit with some games.
To get an idea if a graphics card upgrade will do you some good, run this test:
Run YOUR games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.
If you decide to upgrade your graphics card, make it a significant jump, say to a GTX1060 6gb card, or you may be disappointed.