I get some plots for comparision of different network simulation software. I need to include them in my thesis to provide details about the tool. The problem is that these plots are not of very good resolution and I want to enhance them. Although I must provide the reference of the paper and I downloaded these plots from IEEE library, I am not satisfied with the resolution.
Can anybody please tell me the method to enhance plots. I am including one plot as image here:- 
If you don't like how they have plotted the data, or there isn't sufficient resolution in their graphic (e.g., they used a PNG rather than PDF so that blowing up the document doesn't help resolution) then the only real solution is to ask the authors for a copy of their data, as suggested in the comments above.
You also may consider that if this does not work, the ugliness of their figure is not your responsibility: really, you are only including it as a courtesy to the reader, in order to make your document more self-contained.
