Editing or removing unwanted projects and context's can be done via "long tap" gesture while you are in the Task Edit screen. A long tap is a tap and hold gesture where you don't lift your finger for about 1-2 seconds. When you perform a long tap on a context or project, it is placed into the input field for editing. When you are done click save. Likewise, activating this mode will also bring up a delete button where you can confirm the item to be deleted.
The steps to delete or edit a project or context are: 1. Open the edit mode of a task by selecting a task from a list. 2. In the detail view, click on the document with a pencil icon on the right. That will take you to the edit view. 3. In the info tab you will see the list of projects. Here is where you do the "long tap" gesture that brings the delete button and the ability to edit the name of the project.
The list of contexts is in the filters tab, where you would follow the same steps explained above.
For more information watch this video: http://youtu.be/rW5jGjqMh5c