Edit a task
From the web-app go to 'Tasks', click on the task you would like to edit, after making the changes click 'Save'.
Reassigning a task
From the web-app go to 'Tasks', click on the task you would like to reassign, after making the changes click 'Save'.
Archive a task
From the web-app go to 'Tasks', click on the task you would like to Archive, click 'Edit' and at the bottom left-hand side click the red 'Archive'.