I usually use the regular "paint" program that comes with most all "Windows" Operating System to do my resizing. Right click image, and choose edit, or if you are using a newer Windows OS...You can right click, "open with": then "Paint" (you could also access your "Paint Program", and then choose a file to open from drop down menu ...I find it easy to start with the image, and then go into "Paint".
Up at the top of Paint menu, you will see "IMAGE"...Scroll that menu down, and choose "Stretch/Skew". Then you should see Horizontal: 100%, and Vertical 100%...Just reduce the number of both to exact same number but lower than 100% to reduce the image size (50% in both fields should reduce your image size in half). Then you can go to file, and "Save As"...rename, or replace the old image to save.
This is most likely more info than you were looking for, but maybe it could help others with the need to do basic editing.
Good Luck!