Select the square looking tool on the top left, trace the whole size of the pic with it, then select the menu to cut it, then paste it, select the corner and click and drag it to a smaller size... Hope that helps
When you click on edit, by the picture, you will be taken to the paint screen, you will see an edge to the large picture. Under 'image' choose, 'stretch-skew', then you will see number ratios. The top 2 numbers say 100, delete this number and put 10 in there, on both lines and hit O.K. That will reduce the size. Refile it with a different name and x out the screen. Try that and get back to me.