In FORTE you can delete or customize nearly every score element. Firstly, change to Selection-Mode by pressing CTRL+1 and click on the desired element in your score, for example a note you want to delete. The note will then be marked red. Press the Delete key on your keyboard to delete the note.
When you doubleclick on an element, a barline for example, it will open the Properties-Window. In this window you can make several adjustments to the element as well as editing it's appearance (eg: double barline).