That’s a tricky question. There are thousands of WordPress themes, created by developers from all around the world, each one with his or her own methods of handling default content in themes.
As such, it’s nearly impossible to answer your question without at least knowing which theme you’re using.
Your best bet is to contact the creator of your theme and ask them for support. Go to: Appearance > Themes, then click on your active theme to view the Theme Details, which should include a link to the creator’s page.
Hope this helps!