I have about six computers in my office network,and about four are are heavily infected with viruses and spywares. I have tried downloading the suggested antiviruses by fellow users of this network and have not gotten a solution yet.Someone kindly advise me on what to do.

I would format and reinstall the OS on the infected machines. If these are work machines you do not want a keylogger or spam bot left on a machine because it wasn't detected or couldn't be removed.
You should run a root kit detection program also on the other computers.

Probably not the answer you were hoping for, but it's the only way you can be sure viruses, root kits and spyware are fully removed.
RootkitRevealer v1.71

Also for future security I would consider a product like this to protect your whole office network.
Astaro Internet Security - Astaro Security Gateway Overview

Download CASIR from en.sergiwa.com
It will temporarily Clean All the Infections that are running

Now the Viruses are in a Dormant state
Install Kaspersky (The Best Antivirus Solution) & Run a Scan

Thanx