To move multiple activities at once:
Click the Select button on the tool palette.
Click the first activity that you want to move.
While pressing the <CTRL> key, click each of the other activities that you want to move. As you select activities, each is framed by a group of blue dots to indicate that it is active.
When you have finished selecting activities, click and drag one of them. This moves all of the selected activities at once, preserving their relative positions to each other.
When you have moved the activities to the new position, release the mouse button. Click any blank area on the flow canvas to deselect the activities.