change my hostname

[yohann]

hi
i'm finishing a migration from VHCS on a old server to ispcp stable on a new one,
i' won't say everything is working, but i'm doing my way trought porblems one by one.
but know i'm stuck on this one.
i did a mistake when i choosed the FQDN, it was not a domain i registered, so i need to change this domain name in a domain name i have registred.

i change the domain name in so that
hostname and hostname -f give the right name, but i don't know how to make the change apply to ispcp.

please don't tell me i need to reinstall ispcp from scratch as i already spend on full week in search and configuration

best regards
yohann