Since it takes 3.6 hours to do both front bearing and the bearings costs $42 each then yes they must be pressed on and off. Sometimes you can purchase a ready to install hub, but that is more expensive.
If you don't have the tools, just remove the steering knuckle and take it to an automotive machine shop and have them do the press work. It is not very expensive.
here is a site with good repair info for your Nissan
Hope that this helps!