Your camera should have come with a software to handle image conversation. If you use gimp or photoshop that can resize the file for web resolution.
on pc paint has resize option too you need about 20% size for web
on Mac you have photos can do this too.
web images should not be bigger than 200kb
I use Lightroom and I resize the files all the time. I have never had an issue with anything under 7mb. Since my last edits I haven't been able to upload some and I kept them under 1mb. I am thinking the pixels are the issue like stated before.
I will change the pixels to 1200 when I get home to see if it works.