Here are a couple of options for you:
1. You can use an image resizer to see if that works for what you want to do. Here is a free one - http://www.bricelam.net/ImageResizer/.
2. If you have Photoshop or PaintShopPro, you can resize them in these apps.
3. You can download Gimp.org (free) - here is an article with a little more info on it - https://teamsideline.zendesk.com/entries/21748967-Use-free-GIMP-Software-to-create-image-files-for-your-web-site.
4. You can send the images to us at firstname.lastname@example.org and we can do this for you.