Am using ISA server in my network and i want to replace it with untangle .

My network :

Router : as a gateway
Domain controller : DNS + Active directory
DHCP server
ISA : http proxy
clients brows internet throw isa etc..

I want to put untangle inside my network instead of ISA to let the users take the internet from untangle !

How can i do it and forgive me am not that an expert in network

thanks in advance