The list of tasks for a given project are listed on its Tasks List view
(Project => Tasks tab => Task List)
Project: <Project_Name> - Tasks - Task List
The tasks can be sorted by its displayed attributes on the list (Name, Start, Finish, etc)
To have them ordered as per the project plan, it is possible to use the PPM Gantt Scheduler.
(Open in Scheduler = > PPM Gantt)
This will display the Gantt chart:
Project: <Project_Name> - Gantt,
To have the list of Task reordered:
1. Select the task to be moved.
2. Click on the "Up" arrow button, move.
3. On the pop up select the Task to which the one selected in Gantt will be inserted before or after.
In this example, Insert Before Task Tarea3
The result is the Task being reordered as selected.