A family of Microsoft word processing software products for creating web, email, and print documents.
When you access the header of the document, expand the Select drop down at the right hand end of the Home tab of the ribbon and select "Select Objects" The mouse cursor will change to an arrow head and with that, you should be able to select the watermark that is in the Header and then press Delete.
If you are still unable to do it, send me a copy of the document, referencing this thread in the covering email message, I will investigate the issue.