open it in paint on your computer then select stretch skew.... fill in both horizontal and vertical with a valuee of less than 100% like say 50% would reduce the file size to 1/4 of original.. then select save or save as on the file tab and try posting again
The instructions bond-o linked to will say to get a photo account, like Photobucket. If you choose "resize" in Photobucket, it's an easy way to get the size you want.
