However--unless you have a burning need for 16 gb, 8 is usually enough for a laptop. If you are doing video editing or other ram intensive work, a high end desktop or a top of the line laptop would be better.
Are you sure you only have 4gb? Most 3558 models came with 8. Installing 8 gb would be a good upgrade if you really have only 4--cheaper too. To check your computer--open Settings, System and scroll down to About.