install the one you want to use
go into settings...apps and then find the app that is the default (the one that opens up)
tap that, then scroll down to where it says defaults and hit clear.
Now if you open up some music it should ask you to choose the default player choose the one you want. I am not sure if your options will be just once or always, but you geet the jist, choose always if you want the new one to be your default