Images that are saved at Templates > Album can be replaced in the word processing document via the context menu (right-click). It does not matter whether the images were inserted on the page or in the text flow.
Select the desired image in the letter and right-click.
Select Album image > Replace. A list of all other album pictures that have either the same category 1 or 2 opens.
Select the new image with a left click. The format of the new image is automatically adjusted.
Save your input by clicking on the icon in the top left-hand corner of the input window.