How to resize an image
There are numerous programs that allow one to resize images. Some of them are free and simple, e.g. IrfanView and Pant.NET. These are for Windows.
Below are a couple of pretty good, short video tutorials that show how to download, install, and use Paint.NET to resize images as well as how to determine the current size of files. It covers the entire process pretty well.
If you are using a Mac computer, some of these tutorials may help.