If it is the way you are blowing, then think more of increasing breath pressure as you go higher, rather than tightening embouchure.
If it is a fault with the operation of the mechanism for the two octave keys, then you could see a technician, or do some of your own diagnosis (even cure) using:
http://www.saxontheweb.net/vbulletin/showthread.php?p=312749#post312749
However, this is one of the most complicated areas of a sax to mess with, and unless you understand what you are doing, you could make things worse for the technician who eventually deals with it.
If it is a fault with the operation of the mechanism for the two octave keys, then you could see a technician, or do some of your own diagnosis (even cure) using:
http://www.saxontheweb.net/vbulletin/showthread.php?p=312749#post312749
However, this is one of the most complicated areas of a sax to mess with, and unless you understand what you are doing, you could make things worse for the technician who eventually deals with it.