It is the best way that you upgrade your version of Internet Explorer or use a different supported browser, but if those methods are not available, management is possible in the following way. 

If you sign in as an administrator, not in the administrator mode, a board management(Upload/Move/Delete Post) is possible. Please refer to the URL below.

Managing a Board

http://support.dubuplus.com/Board/15540

Writing and Editing a Post on board.

http://support.dubuplus.com/Board/15538

Replying on board.

http://support.dubuplus.com/Board/15539

Every management is also possible by signing in as an administrator on mobile.

Simply sign in and manage a board on mobile.

http://support.dubuplus.com/Board/15544