1) If an image is larger than 350px in width, you will need to make the image responsive. This is to ensure the image properly adjusts to the width of your browser, tablet or mobile device.
2) Double click the image you want to make responsive so the image properties window appears.
3) Remove the width & height dimensions from the Image Info tab.
4) Next, go to the Advanced tab and in the Stylesheet classes text box type in img-responsive and if you want the image centered use this code img-responsive center-block