To remove all previously selected filters, click the large "X" under the search field at the top of the screen to the right of the filters.

To remove a portion of your selected filters:​
  1. At the top of the search results page, click the smaller "X" next to the item you want to remove
  2. You can now select other filters (product content type, etc) you may want to add to the search and see new results
To restore the saved search results after removing them, launch the search results in a new tab. Your saved search filter will be present.

For more information, review How does the new KB search engine work?