I`m fairly illiterate as well but unless you have a program to do it,this is the easiest way.The most probable reason that a file is too big is usually because its a BMP file.They take lots of space and its easy to reduce thier size by changing the file type....
open the windows paint program-all programs,accessories,paint...
at the top left click on file,open...
now type the name of the photo file you want to post,
or browse for it on your computer.
change the name of it slightly
save as file type JPEG...
click save.
Another thing I love is a free service called photobucket.
Join and it lets you save up to 1000 photos there.
www.photobucket.com
I hope this helps