Modify the Master Slides

Hello,
I chose the template 'Craft' and I am trying to modify the master slide (first slide of the theme).
I succeeded in changing the background picture; however, I am unable to touch, move or delete the white banner in the centre as well as the yellow banner below the white one.
When I try to select the banners, I see little crosses appear around the shapes but I can't do anything with them. Can someone help?
Thank you so much,
Linda