In the Family Tree Builder, removing a note is done in the ‘Edit Details’ window.
Open your tree in Family Tree Builder and find the person for whom you want to remove the note.
Click on the ‘Edit’ button and then choose ‘Edit Details: <Name>’ from the dropdown box.
Click on the ‘Notes’ tab.
The notes you've added appear in this section.
Use the arrow buttons to move through the notes. Use the ‘Delete Note’ button to remove the selected note.