I would like to make a query about the use of the map composer. Sometimes, when I add elements to the map, for example the scale bar, I have realized that I can delete it by pressing only the Delete key (see attached image), while at other times I can not perform this operation. Moreover, I can not even delete the element and I must turn off the layer so that the element is not displayed on the final map.
Reference: https://docs.qgis.org/2.14/en/docs/user_manual/print_composer/print_composer.html
How can I solve this problem?