Resizing wit MS Photo Editor.

Open Photo Editor from the Menu Office Instruments (usually)
Open your image.
Choose "Image" then "Resize". Try to set a width not more than 600 px.
Then save it and in the folder go and look at its dimension, if still big try again the same operation or You can try to cut some borders with "Image" then "Crop".
Pay attention to save it in the standard format .JPG (or .gif).