How do you change a file size for pictures after they are already downloaded to computer?

i have a new digital camera but the files are to big to download them onto auction sites. how do i change the size of the files?How do you change a file size for pictures after they are already downloaded to computer?
You can download this program called PIXresizer . Its really easy to use. I use it.How do you change a file size for pictures after they are already downloaded to computer?
file size can be reduced by making the pic smaller with a photo edit program. It is best to take the pics with a lower resolution setting to get a full size pic but lower kb file size. To put a pic on the web there is no reason to go higher than 1MP as the web can not display a better pic over 1MP. Go a little lower if your camera has a setting for that.
1.) There should be a setting on your camera to allow you to change file size when you intially take the picture.



2.) If you have Microsoft office, you can use picture manager to shrink the file size.



Right click the picture,



Open with MSOpicman



Click Picture



Click compress
You need photo editing software like

Photoshop, Photo Deluxe, or similar.