You can leave it as is. Both sides of the chestpiece have tunable diaphragms which allow you to hear low- or high-frequency sounds simply by adjusting the pressure on your chestpiece (see video here for more). The smaller diaphragm is designed for use with pediatric or very thin patients.
If you only see adult patients and prefer to use an open bell, you can remove the smaller tunable diaphragm and install the nonchill bell sleeve for your patients’ comfort.