Changing a subnet

Hi All,

I have a problem, I have an IP range of 192.168.1.* with
a subnet of 255.255.255.0. But i have nearly reached
250 machines.

This means i am out of IP addresses. What can i do to
fix this. What would be the best solution without
breaking the network segment with a router?

Can you give me indepth detailed instructions on how
to achieve this and you will recieve the points.

Thanks