Question : How to change from CLASS-C to CLASS-B IP Schedule

Currently our Network is on Class-C network segment but it was poorly configured to ALL static ip addresses and NO DHCP at all.  Now our network has extended so far that very soon we'll run out of IP addresses.   I don't have a lot IP management background as it relates to switches and routers, but DHCP configuration that I can do.  Now, the BIG Question is???? what's the process of switching from a CLASS-C to a CLASS-B network segment?   Do we need to hire an expert to do this or it's something I can setup a DHCP and point all the servers, NATed devices, workstations to it?   We've a very complicated network.......our systems talk to other systems around the country 24/7 and all the mission critical applications MUST be ONLINE at ALL Times.
If I need to explain further, please let me know.

thanks,  

Answer : How to change from CLASS-C to CLASS-B IP Schedule

None of your old addresses should change if you just alter your subnet mask. Your current space will be left entirely intact and you will simply have additional addresses. If you have firewalls, ACLs or firewall holes along the way they will also need to have their subnet/wildcard masks changed. But; once you pass the device that does your NAT noone will even know the differance.