2 ways to resize...IrfanView, been using it to crop and re-size my auction photos for years. Fast and simple.
Or if you're uploading on the fly to Imgur for hosting like I do often and want to save a step, you can upload the photo "as is", click on the picture...and at the bottom there's a box where you can select sizes....I tend to choose medium thumbnail...then copy the link in the BBcode box.