You can resize photos and images in many different ways. You can use free online tools or softwares installed on your computer.  Below, you will find links to online tools and video tutorials on how to resize photos in Photoshop and Microsoft Office Picture Manager.  I will add videos for other image editing softwares as they become available.

Resize Your Images Online
Resize Your Images With Microsoft Office Picture Manager
Resize Your Images With Adobe Photoshop

Resize Your Images Online

You don’t need an expensive image editing software installed on your computer to resize your wallpaper images or photos. Wherever you are in the world, you can use the following online tools:

• Wallpaper Resize Wizard: This tool is available on our website. It is a very simple resize tool for any picture, image or wallpaper.
• PicResize.com: This tool enables you to quickly resize, crop and rotate your images. You can also apply one of their 8 special effects.
• Picnik: This is a complete online photo editing software. It offers one-click fixes, including auto- fix, exposure, colors, and red-eye. And the others, like rotate, crop, resize, and sharpening, can be controlled with easy-to-use sliders.

Resize Your Images With Microsoft Office Picture Manager

If you have Miscrosoft Office, you also have the Microsoft Office Picture Manager installed on your computer!
This video shows how to resize an image using this software.

Resize your photos with Photoshop

Of course, if you have Photoshop, you can use it to resize your photos.  You can buy Photoshop online, but it is quite expensive, especially if you will only use it to resize photos.

How To Resize Images In Photoshop CS3 from Nathan Ridley on Vimeo.