To do this, SDRDsharp cannot be running.
Any changes made to the Config file while it's running will be lost when you exit SDRSharp.
Use your favorite editor (notepad etc.) and edit the following file. (After first backing it up.
I usually just append the current date to the file: 'SDRSharp.exe.Config_01-19-2014'
'SDRSharp.exe.Config'
Find the field within the Config file that's highlighted in the screen capture below.
You can change the text between those quotes to be anything you like.
Then, save the file.
Also, anytime you run 'install.bat' to get the latest build, you have to be careful NOT to copy the default CONFIG file back over the file you edited.
Rich