Use a program like Paint Shop Pro or Adobe. Look for a resize button. In Paint Shop Pro you have the option of choosing pixel size. Make that 50. Save it as a jpg file. In "Paint", which everyone has on their Windows systems, I have not seen a way to make the image smaller.
In Paint all you have to do is click on Image at the top of the screen and go to Stretch/Skew. Then just choose a smaller percent. It make take awhile but it works. If you have the other program listed I would do it that way since it is quicker.