Using Matplotlib, changing the size of the figure is quite straightforward.
While declaring the figure and the axes, you can define your figure size using the figsize parameter and pass by a tuple with the width and the length in inches. (e.g. (12,6))
Here is an example
Here you are! You now know how to change the size of a figure with Matplotlib
More on plots
If you want to know more about how to add labels, plot different types of plots, etc... check out the other articles I wrote on the topic, just here :