Uploading a website : I'm uploading a website and there is the previous website there from before?

When i upload the new website nothing changes. Do i need to delete the old website or am I doing something wrong??|||backup the previous website files all and delete it and upload the new one since there are some important files which are only 1 per domain so they need to be changed to new unless they r replaced ya new domain won%26#039;t work.