I’m a PC all the way but what you need to do is the same - in whatever editing program you use, you need to learn how to a) resize the image, making the entire thing smaller without cropping parts of it off and then b) lower the resolution/quality of the image. Most programs out there have step by step tutorials somewhere on the internet.
Basically, the file that comes out of your camera is high quality so that if you want you can make a massive print to hang on your wall. For casual internet viewing, a much smaller size and quality are acceptable and also necessary unless you want to spend an eternity waiting for giant files to load.
On this forum you can’t directly attach photos to a post anyway unless you pay for a premium account. I would suggest uploading to a website like Photobucket which will resize the photo to a reasonable level for you, then post the link here.