Image Size

Hey, im not really sure if this is the corect place to post this but w/e. Im trying to load up an image onto my guilds website but its a big file (almost 5mb). Im looking at the dye charts and they are even bigger that what im trying to do. What i really need to know is how do I change the file type to make this smaller?

Find a program that will convert the file to JPEG (.jpg) format.

i dont even know what that is... Only way i knew how to do that was though image shack but these files are to big to use on that site.

I found this but im not sure how to use it. Ive gone though it and it doesnt do anything for me.
TotalImageConverter 1.0

Easiest is to pop up Paint that comes with windows (Start-menu -> Run... -> type 'mspaint'), then open up the image (File -> Open..), then select "Save as..." (from File-menu) and switch "Save as type" from BMP to JPG.