This window has 2 parts: a title bar and the navigation tabs.

• The title bar tells you where you are in AceProject. At the end of the title bar you will find links to the contextual help, to add a new task, to open or close a time counter, to move/copy a task, and to show a printer-friendly version of the page. 
• The Task tab shows all available data for this task.
• The Assignment tab shows which users are assigned or reviewers on the task.
  • Simply check the boxes next to the users who will be assigned and/or reviewers on the task.
  • You can select as many assigned users or reviewers as you want.
  • You can un-assign the users simply by un-checking their boxes.
  • Whenever there is a change in the users assigned to a task (new and removed users), the task's Last Update field will be modified.
  • Check the "Do not send email notification" box to avoid sending an email if the update does not warrant it.
  • Click the "Update" button to save your changes.
  • Click the "Update + Attach" button to save your changes and go to the "File Attachment(s)" tab.
  • Click on the "Back" button to return to the "Tasks" page without saving anything. 
• The File Attachments tab  displays all files attached to this task. 
• The Dependencies tab displays all relationships between this task and other project tasks.
• The History Trail tab displays all changes to your task since its creation.

How do I remove/un-assign a user from a task?
You can un-assign the users simply by un-checking their boxes and clicking the "Update" button.