You can remove a widget using the Service Portal Designer.
1) Navigate to the page that the widget is on currently.
2) Control + click on the widget (or any widget on that page) and select "Page in Designer".
3) Once the page loads, hover over the widget you want to remove. You should see a small trash can icon in the top right of the widget.
4) Click the trash can and then confirm you want to delete the widget. This does not delete the actual widget but only the instance of it on that page.
If you want you can also remove the container that the widget was in by clicking the container and then using the Trash Can button on the top right of the page.
Here is how to add widgets to a page.