Sketch theme, how to make the page title disappear

Hello, I am currently building my site with the sketch theme and I can not manage to get rid of the page title and the thin grey line underneath the header… (all my pages are either set to Portfolio type page or to Full width/no side bar). I would like to see simply the header with the name of the site and the menu to the right, and the thumbnail images underneath. On the portfolio page there are even two grey lines that appear between the header and the images. Could you please help me to delete those 2 lines?