Hello Fiona,
server all of the others connect to meaning? Directory server?
What I would do.
upgrade to 8.0 sp3 (or sp4 if that fits your timeframe)
check it is ok.
check the disaster recovery part in the admin guide. If you are using aliasses for the vaultservers, it should be relatively simple.
from the top of my head. on server to be removed, disable ev-services (so they do not start when booted) Shutdown ev, install new server (new name), change dns so alias points to new server. start new server (attaching disks etc obviously), verify ev starts correct. start remaining 3 servers, verify ok. start old server, uninstall ev.
DR plan has more precise and outlined steps.
Regards. Gertjan