Thanks Elliott once again.

I have already default instance and we called by ip or DEVDB then iinstalled sql 2005 and created another instance as named instance - STG so it's called DEVDB\STG becuase sql server can have only one default instance.

By mistake, i forgot to change the default location for files so all system DB created and using C drive.

How can I change the location? Should i leave the system DB there and create another MSSQl directory on D:\ drive like files - D:\Program Files\Microsoft SQL Server\MSSQL.2\MSSQL and when i create/Migrate new DB then change the .mdf and .ldf location to new path?

If i migrate DB then it will go to old location where my system DB files are, right?