You can change an image of your landing page and replace it with one from your gallery or upload a new image (all images you upload will be part of your gallery).
To edit an image, simply click on it and then click on the "Edit Image" link that will appear on the top of the image. Select or upload a new image and hit save.
Editing a piece of text is very straight forward, and very similar to any other text editor you have used. Simply click on the text that you need to edit, and you will be presented with a few options to change the font, size, color, alignment etc.
If you need to edit a call to action, change the text or the url, all you need to do is click on the link and then click on "Edit Link" option that will appear on the top of the link.
After that you will be presented with a few options to change the text or the url of the link.