Change Domain Controller

I need some opinion or guide as to how i should approach this. We just took over a company (oldlocal.com). And would like to change the name of the DC to the new company name (newlocal.com). Currently all client pc’s log on to the domain oldlocal.com to get access to files on the file server, internet, pmserver …

we have 5 servers in the oldlocal.com domain.
1) File server (DC)AD
2) Accounting server (member server)
3) project mserver (member server)
4) web server (member server)
5) print server (member server)

and have about 20 desktop pc’s

i just want to be able to have the 20 computers to logon to newlocal.com

** i have a6th server sitting doing nothing. **