Syncing MIDI notes and audio parts to tempo

What is the method to sync for example some MIDI bass notes and kick drum samples to the tempo if I decide to change the tempo?

You need to ensure that the tracks you want to have follow the tempo changes are set to ‘musical’ mode.

To do this in the Project window, select one of the tracks (midi or audio) and check the box in the Inspector that contains a musical note.

That should do it, but if it does not for the audio parts, double-click on the parts to open them in the editor and click the same box there.

good luck.