Answer

Check to ensure that the transport pin has been removed.   Height should be adjustable after that.

Here is an example of a display with the transport pin still in place:

Here is a close up of the pin:

Refer to page 6 of the user guide for details.

http://www-307.ibm.com/pc/support/site.wss/document.do?sitestyle=lenovo&lndocid=MIGR-73608