George,
Go to
www.psrtutorial.com and you'll find step by step instructions for just about everything that can be changed or adjusted.
Essentially you can change any instrument on the fly.
1. Select the style you wish to edit.
2. Press the mixing console button twice.
3. Press the numbered key below the instrument you wish to edit or change.
4. Select that instrument and you will hear it change.
5. If you wish to save the changes, you'll have to do this in a registration file. Then each time you access that registration, the changes will be accessed for that particular style as well.
Cheers,
Gary