Double-click on your JBoss server to open the Server editor. Go to the second page (Deployment) and at the top of the page you should see THREE options. 1) Workspace Metadata. 2) Server-relative path, 3) custom
For Workspace metadata or server relative path, the text boxes for "Deploy Folder" and "temporary deploy folder" should be disabled (not editable). However if you click 'custom' you should be able to modify these fields.
Legend! Thanks Rob!