8GB of RAM is plenty for games and Skype. If you were doing photoshop or developing large database, then you should upgrade your RAM.
As JobCreator stated, if your laptop only has 1 stick of 8GB RAM, then upgrading your RAM can increase overall performance a little bit. That's because when only 1 stick of RAM is installed it is only running in single channel mode; half speed data transfer. With two stick of RAM they would be operating in dual channel mode; full speed data transfer.
Using two stick of RAM with the same RAM size means they will be operating in synchronous dual channel mode. You will get about a 10% overall performance increase compared to single channel mode; roughly speaking.
Using two RAM sticks of different sizes means they will be operating in asynchronous dual channel mode. You will get about a 8% overall performance increase compared to single channel mode; roughly speaking.