Migrating from x86 (32) to amd64

[Artem Kuchin]

Maybe someone could help me.
I have a machine with 4GB of RAM 128MB of which is wasted and i really 
need 2 gigs more.

This is a heavy duty production server with a lot  of jails and custom scripts, etc..
and i am afraid i cannot reinstall all from scratch. Furthermore it is located in the
data center away from the office and i simply cannot spend whoel day there, but
2-4 hours would be ok.

Currentlyt it is 5.4-STABLE (i386, 32bit architecture)

Is there way to more or less sefely  migrade to AMD64 arhitecture via csup and
source build?

Any recomendations?

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Regards
Artem