If it is sketchup, if I may further suggest something.
It's easier if you just go File -> Export -> 2D Graphic
Then it will save a render of the screen only (not the user interface) and you can select the output image format there aswell.
png would work, but jpg is even smaller, so whatever you need to get under the allowed maximum size, will do. You can always experiment with the various file types.
Allowed file attachments on this forum are: doc,gif,jpg,mpg,pdf,png,txt,zip,dat,img,xls,csv (obviously not all are image files)
Fred