That one command Loyce has provided before your reply is all you need.
Everything that could conflict are already pre-configured to use separate/different values by default.

For more simpler guide (if you're on Windows), check this thread in 'Beginners & Help' board: /index.php?topic=5215716.0#post_actsteps
Note: --testnet is for "testnet3", --testnet4 is for the latest testnet, there's also --regtest for other testing purposes that can be done locally.