As you use a 3d printer, over time the printing bed can be slowly pushed away from the extruder, which messes up your prints in all sorts of different ways. Fortunately, re-leveling your bed is easy and takes no more than 5 minutes.
To start, turn on the 3D printer using the switch on it's back. Once the printer has started up, go to Utilities>Level Build Plate. It will then begin the leveling process and display directions on how to do it. The extruder will move to different points on the build plate, and you will need to slide the small card by the printer uder the extruder head and tighten and loosen the knobs underneath the build plate until you feel a smalll amount of resistance. This will need to be done for each point on the build plate that the extruder moves to. Once it is complete, the printer will be ready to print on once again.
For more information, visit https://support.makerbot.com/learn/makerbot-replicator-2x/getting-started/leveling-the-build-plate_11702