I am using sony a6000 and most of the clicked image size are below 1 MB. I want it to be above 4 MB so i can upload in shutterstock. thank you.
Based on the comments seems like you set your camera to take small images (in JPEG format). To get bigger images follow this page and set your camera to L size.
Also Sony use a bit aggressive compression for JPEGs so you can set your camera to shoot RAW and then edit your images and export them with low compression. This will help you to keep more colours.