The Default Instance of SQL Server Runs on Port 1433. The default instance of SQL Server does not support dynamic port allocation. However, the named instances of SQL Server support allocation of both static and dynamic ports. By default, a named instance of SQL Server listens on a dynamic port.
If you are working on a Named Instance, the SQL Server Browser service (in case of SQL Server 2005/2008) or the SQL Server Resolution Protocol (SSRP) (in case of SQL Server 2000) is always used to translate the instance name to a port, regardless of whether the port is static or dynamic. But Browser service or SSRP is not used for a default instance of SQL Server.
If you are running a Named instance and want to change the Port No., you can configure SQL Server to start listening on a different Static Port via. SQL Server Configuration Manager. All you need to do is go to SQL Server Configuration manager delete the value from TCP IP Dynamic Port and enter the desired Port No. in TCP Ports Field. This change needs a Restart of SQL Services.
Please refer the screenshot below: