howto upgrade fc3 to x86_64?

["sean darcy" <seandarcy hotmail com>]

I'm running fc3. Just got a new athlon64 macine. Just moved over my hard 
drives. Works fine.

Now I want to convert/upgrade the fc3  from i386 to x86_64. I'd really 
prefer not to do a clean install - I'll never remember how this machine is 
set up.

thanks
sean