Remove “Category” in navgation and header text

Hi, I'd like to remove the text "Category" from the navigation and header text. For example, instead of displaying "Home>Category: Teaching Materials", I'd like it to display "Home>Teaching Materials". Same as the header text. I only want to display "Teaching Materials", rather than "Category: Teaching Materials". Is there a way to achieve this? Thank you. Here's my example page: http://piigut.sgedu.site.