If youre talking about reducing the size of photos before posting them, You probably already have the software, if you are using a windows OS

Select the pic you want in its folder, and right click and choose "open with", then "paint".

When the pic opens in paint, select "Image" on the toolbar, then "Stretch/Skew"

When the Stretch/Skew window opens, reduce the percentage a bit at a time, until you see the size of the photo get down to the size you want. Remember to copy the pic to a separate folder to shrink or your original will be shrunk when you save it. When the pic is small enough to look good on that screen, it is usually the same size on the web page youre going to upload it to.

Go in even percentages like 80% & 80%, 50% & 50% etc or you'll get the squished look like on TV when they mash a wide movie into a square screen.

Ive found that once you shrink the size of a pic however, if you try to enlarge it after going too small, if you try to enlarge it the same way, the pixels blur as it increases in size, so go in small percentages at a time until you get used to how it reacts.

If this isnt what you were talking about, please disregard this message.....lol
Hope this helps.