To edit a task, just click on it (from your tasks page or the process page itself).

When you click on the task, the edit window will appear:

From here, you can reassign the task, change the description or task type, change the due date/time, give the task a priority, or set a reminder.

For email tasks, you can also set them to go out automatically or change them to a manual task.

Note that editing a task on your tasks page or on a process will not affect the process template itself. Touch base with an admin on your account to make permanent changes to the process.