Delete

Select the bracket and press Del

Add

Drag a bracket symbol from the bracket palette to an empty space in the first measure of a system.

Change

Drag a bracket symbol from the bracket palette to an bracket in the score.

Edit

Double click on a bracket to enter edit mode. In edit mode you can drag the height of a bracket to span arbitrary staves of a system.

Horizontal offset

If you need to move a bracket further left or right then double click the bracket to enter edit mode, and press Shift+Left or Shift+Right.