Steph--I use this program
http://www.irfanview.com/ It is free and easy and (best of all!) works very well. Once it is downloaded, click on "file" and then "open" Once you have the picture opened, click on "Image" and then "resize/resample" Make sure the box at the bottom that says "preserve aspect ratio" so that the pictures don't look out of perspective. You can set the size in pixels, cms or inches. Once the picture is resized, click on "file" and "save as" to save your newly sized picture.
HTH
Linear Mode
