Post blog image size

MaximPhotoStudio

All of my posts are limited to a boxed width. I am trying to increase the size of my images on the blog posts to 1000px or 1200px, etc or make it full width so I can insert a gallery. I don't see an option to do this. How do I do this? I size my images to 1,600 px width. Here is a post for reference. https://maximphotostudio.com/puerto-rico-destination-wedding/

Thanks