1. download paint.net image editor (free)
2. install it
3. open up image to resize (drag and drop into paint.net)
4. click Image > resize
5. It is best to maintain aspect ratio so the image resizes accordingly
Type in the width you want; the height will automatically be filled in
6. Click OK. The image will be resized
7. click File > Save As...
8. Choose a different filename for the resized image. I always use lower-case and no spaces. I use dashes to separate words. Mixing lower and upper case can cause confusion on Linux servers (which you are on).
9. It will ask you for quality if you're saving as a jpg. I use 70 or 80.