1. If you are using a hub, replacing that with switches will reduce the delay in case many users simultaneously access the network, copy files etc.2. Firewalls and antivirus software's cause network delay. If you have some AV of firewalls installed, uninstall it and check the speed. If you find improvement, u can install a better AV although that will cause delay to some extent.3. Virus / malwares cause network delay. Reinstall the OS, use some updated AV, and check it.4. If you mean delay in Internet connectivity then you have to go for greater bandwidth.