An option that you can specify when ordering your roller conveyors or pallet conveyor system is to have removable rollers.
The options for removable rollers can vary from having rollers where the pins in the ends of the rollers are spring loaded (Push the pin back to remove the roller) to having special cut outs in the frame so that the rollers can easily be removed from above (See picture).
While this is an obvious advantage where the roller is broken or the bearings fail. it's also a useful feature for when routing maintenance needs to take place, because removal of rollers can sometimes be useful to gain access to motors and other equipment.