To modify a task list, click the pencil icon which appears when you place your mouse over the name of the task list:

The only information associated with a task list is the title and the workspace the task is associated with.  You can modify the workspace to move a task list from workspace to workspace.  If a set of tasks in a workspace is getting too complicated, you may want to split the tasks into separate task lists, and move those lists to other workspaces.

If you click the name of the task list, you can also click the "Edit" link in the upper right to modify the task.  Both methods allow you to modify the same information.