How do I replace my western saddle's fabric?

I got my first saddle out of my barn and cleaned it up really good and it still needs a few things like conchos and the leather needs more cleaning and the fabric on the seat looks gross.. I found some fabric to replace the old fabric and all I need now is someone to tell me how to sew on the new fabric and what I need to do this. Do I need to take the saddle apart to do this? I'm artsy and I like to do things myself and I don't wanna take it to someone and spend a fortune. Thanks:)