how to delete a legacy extension

You don't need to delete legacy extensions, as yet, unless they prevent the computer from starting. First, locate where the extension is stored. Select the extension, then CTRL- or RIGHT-click on the selection and choose Move to Trash from the context menu (do not try dragging the extension to the Trash.) You will be prompted to enter your Admin password.

Legacy extensions may be found in several locations. To assure they are removed you should simply upgrade the software that installed them.

See About legacy system extensions - Apple Support.