getpaint.net - Paint.net is a fabulous free program for doing basic edits. I do 90% of my bitmap image editing with it.
You might be able to get round the filesize limit by simply going to File > Save As,
type a different filename (so as you keep the original), choose JPEG as the file type, then click [Save]. A box will pop up asking you what quality you want to use, and the file size produced by using that quality setting will be shown at the top of the box, in the middle. Get it just below the limit, and ta-da!
If thats not enough, you need to physically reduce the size of the image through:
= File > Open and choose the file
= Image > Resize
= You can then choose the size of the image
Then follow the instructions above with regard to Save As... and generating a new JPEG file, making sure that the filesize is under the limit.