It's a param in /path-to-your-web-root/parameters/your-server.tcl:
ns_section ns/server/${server}/acs
# who signs the average user-visible pages
ns_param SystemOwner yourname@yourdomain
# who signs the admin pages
ns_param AdminOwner bossname@yourdomain
There is an amazing number of useful configs in this file; you should spend some time learning what everything does there, IMHO. HTH.