Comfort bikes can be very heavy, but a lot of them also have suspension. The suspension can handle a curb (at least I found it could). Just pull-up on the handle bars when you hit and make sure to pedal through it. You don't need to be going fast, if you need to slow down, that's fine, but when you approach, pedal over the obstacle--the traction from the rear tire will help power the bike over the curb.