To reduce the picture’s size I suggest this small and free program, called, irfanview
http://www.irfanview.com/
Once installed, launch it and open, through the program, the picture you need to resize, clicking on the small folder under "File"
Now select “Image” and then “Resize/Resample”
In the new window select a custom size or use the size presets on the right (like 640 X 480)
Now select “File” (top left) and “save as”. Change the name of the picture (so you’ll not modify the original) and save it wherever you want
Just check that the bar on the right panel is on “best”, so you’ll not loose quality, and that it is a JPG file, for maximum compatibility.