To edit a PDF document, open it with Adobe Acrobat. Once opened, click on the Tools located in the upper right corner. There you will see several options used to edit an existing PDF document.
If you need to edit (change) a banner, which is a picture, expand the Content Editing section and click on Edit Text & Images. Adobe Acrobat will scan the document and mark all pictures and text. You can then move existing banner (picture) or you can delete it and add a new one.
To add a new picture, click on Add Image, also located in the Content Editing section. Browse to a location of the desired banner and select it. You will then be able to resize it and place it whenever you want.
You can do the same with text.
When you are done, click File and then Save As… and give your document a new name, so that you can keep the original.