Need more IP Addresses

My network is running out of private IP addresses, currently i am using 172.20.0.1 with subnet of 255.255.254.0.
What is the best way to expand the dhcp server for more ip addersses with out disturbing existing subnet?
I need at least 200 IP addresses more and the users have to get the ip addresses from the same DHCP server.
I really appreciate any help.
Thanks in advance.