How do I convert my Garrys mod server from Sandbox to DarkRP?

[Wefewf Wefwef]

so say i put my server.cfg text in C:\srcds\orangebox\garrysmod\cfg and i have darkRP (not sure which version) in C:\srcds\orangebox\garrysmod\gamemodes and when i reload the server it stays as sandbox, how do i get to to convert to darkrp?