How to upgrade the ssh program on OS X 10.6.8?
Note that ssh on OS X is part of the default OpenSSH suite included with OS X. So to upgrade ssh you should upgrade the entire OpenSSH suite of programs to get a newer version of the ssh program.

Check out the OpenSSH Portable version


Download load the version you want.  


  The portable OpenSSH follows development of the official version, but releases are not synchronized. Portable releases are marked with a 'p' (e.g. 4.0p1). The official OpenBSD source will never use the 'p' suffix, but will instead increment the version number when they hit 'stable spots' in their development. 

Read the Installation instructions carefully, before installing.


As noted there:


  The OpenSSH provided here is designed to run on the following Unix operating systems:
  
  AIX
  
  HP-UX
  
  Irix
  
  Linux
  
  NeXT
  
  SCO
  
  SNI/Reliant Unix
  
  Solaris
  
  Digital Unix/Tru64/OSF
  
  Mac OS X
  
  Cygwin
  
  ... and more are being added all the time.