Change work complete or percentage complete

From the task table

Change the value in the Work Complete or Work Complete Percent column.

Note: When changing the value of Work Complete to a nonzero value, the task status is automatically changed from Not Started to In Progress.

From the Gantt chart

Click and drag the left inside edge of the task bar and drag the dark blue duration bar to the right within the task bar. Your mouse cursor changes to a hand pointer. Dragging changes work.