Pictured above is one half of the upper and lower bearing assemblies. The longer one belongs to the upper guide, and the shorter one belongs to the lower guide.
Tools you will need: Pliers or something else to grip the knurled knobs, 2mm allen key (Not pictured), and a vise to hold the assembly still while you remove the knurled knobs.
Put the bearing assembly in your vise. Then with a pair of pliers, twist off the knurled knob. Once you have the cap loosened sufficiently, you can remove the knurled knob and take off the bearings.
Here is the bearing assembly fully disassembled. There are two bearings, and two spacers/washers per assembly.