I'm going to assume that you are currently using a class C network, hence the problem - you have 253 hosts and so your network addresses are nearly saturated.
If this is an 'official' network, i.e. it's address has been assigned to you and you are using the addresses to access the internet, then the time has come to re-address your internal hosts.
Ranges of IP addresses for each class have been reserved for private network use - these addresses will not be routed over the internet:
class c : 192.168.0.0 - 192.168.255.255
class b : 172.16.0.0 - 172.31.255.255
class a : 10.0.0.0 - 10.255.255.255
When renumbering your network, I would suggest that you allow for future expansion.
In order to calculate the subnets you will use, you should use the calculators at http://www.subnet-calculator.com/
If your network is already configured with addresses from the above ranges, then you will need to add another (or several) subnets to your LAN config. In this case, now is the time to take a look at you network design and perhaps think about subnetting.