Within Teamwork Projects you can edit tasks from the breakdown view which can be found in the overview section of your project.

To do this click on the Overview section of your project, then select the summary section.

You will then see the option for breakdown to the right of the screen. 

The breakdown shows the total number and proportion of active tasks that are assigned to each person on the project. You also have the option here to switch from a breakdown of active tasks to a breakdown based on estimated time.

You can get a more in depth view and the option to edit these tasks by selecting the quick view button.

When you select quick view, a window will pop out to the right showing a list of users along with the task lists on the project.

When in this view, you can click on a task to edit its details and also assign to a different user.

You can filter which tasks are shown by selecting a user from the list to the left.

You can also switch between active tasks and estimated time here using the dropdown near the top left.