You are able to upload and organize images for your landing pages from within the image gallery. To access the Image Gallery, click the 'Add Image' tab from within the landing page editor and drag it to the desired location on your landing page:

Then, double-click on the element to access the Image Gallery.

From the Image Gallery you can upload individual images (or sets of images in bulk), and organize your images into folders for easy sorting.

Once you have decided upon the image you would like to add to your landing page, highlight it and click the red Select Image button.