I changed my sources list to point to testing and then (with a deep breath and confidence data was backed up), hit apt-get dist-upgrade. When I did it, it was only a few weeks after Etch was "fixed" so the updates have been gradual. But that is the process I used, although there may well be seasoned users who would recommend a different strategy.
I upgraded to lenny by apt-get dist-upgrade. As of now its working fine. I think it will take time for me also to know if some problems exist. Regards -- G V Manu