Can Botox change my round face to a long face?

BOTOX®
works by temporarily paralyzing tiny facial muscles responsible for creating
dynamic wrinkles like crow’s feet or frown lines between your brows. However,
it doesn’t add volume and can’t be used to change the shape of your face.
Dermal fillers can add some definition to enhance your appearance, but the goal
for injectables is really for subtle improvement not a dramatic change. If
you’re young, the shape of your face may take on a longer look as you grow
older and fat distribution throughout the face changes somewhat.

If you have a wide jawline Botox can be injected into the masseter muscles to relax them. This gently reshapes the jawline to make it more narrow. Fillers can also give you more definition in your cheekbones. However, to determine what would be the best for you, please see an experienced injector.

To a certain extent, a combination of Botox and fillers can change the shape of your face.  Without examining your face, it's difficult to answer definitively, but in general Botox for masseter reduction will be able to narrow and taper the lower third of your face.  Using fillers to enhance the cheeks and the chin can further contribute to lengthening and slimming the appearance of your face.