'file-size' and 'Image Size' are not quite the same thing.
The Image size, is the number of pixels, or MegaPixels, the little coloured mozaic squares that make up the picture; so many squares wide, so many tall. More of them, the bigger the image.
The file size in Mega-Bytes, is the amount of computer 'code' used to describe those pixels that make the image, that is stored on the camera or computer.
The relationship between the two is a long way from directly proportions. More pixels would tend to demand more data to describe them, but the format the data file is in, and the amount of 'compression' it uses as well as the amount of detail in the actual picture all have influence.
This tutorial explains it in more detail.
Understanding; Mega Pixels, Mega Bytes; tif, jpg, bmp, nef, & raw?
Answering your question, however, for most 'upload to web' purposes, images generally need to be in jpg format, and sized to a pixel count of no more than about 1000 pixels on the wide-side.
Even set to the 'small' image size, as shot, your camera is probably making pictures that are many times larger than many photo-hosting sites will accept! Crikey, even the potato that pretends to be a camera in my antiquated mobile-telephone makes pictures with a pixel count that need to be 're-sized' in a photo-editor on the computer before I can up-load them to many places!
As other advice, you need to use a photo-editor on your computer; open the photo from file, use whatever 're-size' option it has to change the pixel resolution to about 1000px on the wide side, and then save with a new file-name to avoid over-writing the original photo, in the jpg format for most applications, and if your photo-editing software has the option, you may be able to select the 'compression' rate, to make the file size even smaller for easier electronic transmission, though many host sites apply their own compression when they save your picture to their server anyway.