Related Questions:
How do we edit/change the pictures in the hotel proposal?
How can I modify the photo on a document?
Procedure:
In Settings, click on Templates & Files
Click on Documents Templates
Select the Document you wish to Edit
Click on the edit icon on the image you wish to replace
Click Choose File
Select which image you'd like to insert from your computer
Optional - customize padding, width (size) and alignment
Click Apply
Click Save on your Document Template