Edit : As i did a little playing around on Metamask plugin i could see how to change 
Localhost is nothing to do with your question unless you try to connect remote Ethereum clients which are running on Robsten. It looks like you are using Metamask's plugin as an Ethereum client (you can use Geth or Parity too). If this is your case you will continue use localhost to connect your Ethereum client and change check blockchain network as it is documented in Github repo of MetaMask :
web3.version.getNetwork((err, netId) => {
switch (netId) {
case "1":
console.log('This is mainnet')
break
case "2":
console.log('This is the deprecated Morden test network.')
break
case "3":
console.log('This is the ropsten test network.')
break
case "4":
console.log('This is the Rinkeby test network.')
break
case "42":
console.log('This is the Kovan test network.')
break
default:
console.log('This is an unknown network.')
}
})
In case you are using Geth client you need to run your Geth client with : --testnet
flag, or if you are using parity you need to use --chain ropsten
flag. Check documentation for further reading.