When you tap your home key, and you have multiple home launcher options, a window will pop up asking which launcher you'd like to use. You can also choose which one will be default there. If you want to change your default, the only way I've found is removing the current default or installing a new home launcher, though there's probably a proper way that I haven't figured out yet. I usually keep multiple launchers on my phone, and use Home Chooser Flow to select the one I want to use.