Upgrading your RAM to 8GB can be helpful. As stated with two sticks of RAM the RAM will be running in dual channel mode rather than single channel mode. That basically means that with only one stick of RAM data transfer between the CPU / graphics core is at half speed. Going from single channel to dual channel doubles the transfer rate, but that does not mean your laptop will be twice as fast; 10% - 15% performance increase would be reasonable though.
If you are relying on the integrated Intel graphics core to play games with then it is highly recommended you install another 4GB stick of RAM partially to get a bit more performance, but also because both the iGPU and programs and OS will be sharing the 4GB of RAM.
In general games...