If you need to change/update the properties of an activity simply hover over the item in the Gantt Chart and double click on the item. This will bring up an Edit Activity popup.
From the popup, you can update the information, activity type, functional area, assignees, and the Date & Time/Duration of the activity. You can also delete the activity by clicking on the red trash can button, or copy the activity by clicking the copy button beside the green check mark.
You can also use drag and drop tools to change date of an activity from the Gantt View. If you hover over an activity and drag the item to the left or right then release the item, it will snap to the closest grid line and change the dates of the activity.
Or to quickly change the duration of a task, hover over the item on the Gantt Chart and on either end of the task a grey bar will appear. Click and drag the grey bar to change the duration of the task, when you release your finger from the mouse it will snap to the closest grid line.