At the uploaded server you have a connection string for that server..
right then copy that string and add or replace it with your connection string in web.config file like this
1) old web.config looks like this at local system
<connectionstrings>
<add name="CONNECTION STRING NAME" connectionstring="YOUR OLD CONNECTION STRING" catalog="YOUR" database="" security="True"<br" mode="hold" /> providerName="System.Data.SqlClient" />
</connectionstrings>
2) Now when you got upload your site and configure your database at remote database server got the connection string from that database copy that to here
<connectionstrings>
<add name="CONNECTION STRING NAME" connectionstring="YOUR NEW CONNECTION STRING" catalog="YOUR" database="" security="True"<br" mode="hold" /> providerName="System.Data.SqlClient" />
</connectionstrings>
After doing this you can access your database connection string using this command in your code behind page like this
using System.Configuration;
string con = ConfigurationManager.ConnectionStrings["YOUR CONNECTION STRING NAME"].ConnectionString.ToString();