I've searched and read a few things about "upgrading" to 64 bits, and it seems that the only solution is to make a clean install.
I have /home on a different partition, so it's ok for my personal files.
Which other parts of my systems should I backup in order not to loose any data ? I've seen that apache and sql have some data in /var, so I think I should backup this one... and of course /etc too...
And anyway... once I have installed the "new" 64 bit system, will the files from the "old" /etc and /var be compatibles with the 64 bit system ?