The method for closing a Sequence / Independent Screen is as follows :
  
1> Select the particular Sequence or Independent Screen you want to
close by clicking left mouse button on it.
  
2> Click right mouse button on the selected Sequence or on the
selected Independent Screen and a menu window pops up.
  
3> Select "Close" menu item to close the selected Sequence or
Independent Screen.
  
4> Sequence or Independent Screen can also be closed from the
File menu ie. Select "File > Close > Sequence > sequence name"
or Select "File > Close > Independent Screen > screen name".