IP Address

Currently, I am supporting extimated 100 users that will eventually grow to 400 users. I am planning to change the IP address from 10.10.10.1/100 to Class C IP address(192.168.1.1/100). The Router (Cisco 2600) is currently using 10.10.10.15. How do I go about it with out causing any damage and do what do I need to change in the router? I have also 6 Servers that need to be changed.