Serum.

I just bought Serum and have it on my SONAR. While the serum keyboard makes all the noises of the presets the way it ought to, I do not know how to get any track on songs to convert to a selected pre-set (for example, a piano that I wish to sound like something else via Serum). In fact the sound on a track won't be heard if Serum is on as an effect on that track but can be heard in its original form if I press by-pass. Was Serum not meant for this ?   Nice sounds in that case but a waste of money ?Thank you.