Take the appropriate action depending on the dialog box displayed.
To save the change, do one of the following:
Click on another row in the window.
Click 
Save
Click File » Save
Press Ctrl+S
You can delete one cell or a group of adjacent cells. Adjacent cells can run across one or more WBS elements.
To delete one or more cells, complete the following steps:
Select the cell(s) you want to delete. To select more than one cell, hold down the left mouse button and drag across the cells.
To initiate the delete, do one of the following:
Click Edit » Delete Cell(s)
Press the Delete key
If the cell affects status (Complete and % Complete fields), and you have not yet set the As Of Month, MPM will display the As Of Month dialog box.
If the cell affects earned value (Weight field), MPM displays a dialog box asking you to confirm the delete.
Take the appropriate action depending on the dialog box displayed.
To save the change, do one of the following:
Click on another row in the window.
Click Save
Click File » Save
Press Ctrl+S
You may be prompted to confirm the save.
If you do not want to save the changes, press Esc.