Your browser saves copies of images, stylesheets and other website files so pages can load more quickly the next time you visit.
Most of the time that is useful. Occasionally it means you keep seeing an older version of a page after changes have been made.
Before clearing everything, try a hard refresh first.
On Windows press Ctrl + F5. On a Mac, try Command + Shift + R. This is often enough to reload the current page without clearing your whole browser history.