Rebuilding everything

[Vittorio]

As a newbye with freebsd 5.3 on a pentium 3 and many source packages compiled 
& installed from the ports, I've just learnt that I could "tailor" my box 
modifying make.conf. I'm focusing now on the fact that I could add a 
"CPUTYPE=p3" in that file to make the all box faster due to a more refined 
compilation.
BUT...
How could I re-compile and re-install everything to take into account the new 
directives in make.conf?
Ciao
Vittorio