In Microsoft Project, there are two scheduling modes: automatic and manual. By default, a project is in automatic scheduling mode and roll-up values are automatically recalculated. If, for some reason, the project is in manual scheduling mode (see Manual Scheduling Mode in Microsoft Project), then you can do one of the following:
Set the project to automatic scheduling mode.
F9to recalculate roll-up values.
Note: If the work plan is Project Management-controlled, you may not want to recalculate the roll-up values. Recalculating the roll-up values results in changes to project dates.