To convert the default extruder from using 3mm filament to 1.75, you'll need to disassemble the default extruder.
Disconnect Extruder Mount
Disconnect the cable from the extruder that contains three wires for the fan, motor and heater block.
Remove Extruder Mount from Gantry
Use a 2.5 mm hex bit
to unfasten the screw and release the extruder mount assembly.
Remove Fan from Extruder Mount
Unfasten the two screws that are holding the fan to the extruder mount.
Turn to the mount on it's side, switch to a 3mm hex bit and loosen both screws from the assembly.
Move the extruder and motor aside. The metal mount plate is attached the nozzle and heater block.
Unfasten Two Screws from Budaschnozzle
Remove the mount plate by unscrewing the the two 2.5 hex screws from the wooden aligners.
Remove Metal Plate from Budaschnozzle
The mount plate is aligned to PTFE tube, use slight force to pull the plate off.
Detach PTFE Tube from Isolator
Use a side to side pulling motion to remove the bottom PTFE tube from the PEEK Isolator.
PTFE Tube removed from Isolator
Take care not to bend any of the wires to the heater block.
Use a sharp needle to poke out the left over filament remaining around the PEEK Isolator.
Remove Heat Sink and Washers
Slide each heat sink blade and washer off the PTFE tube one by one.
Replace PTFE Tubes
Switch out the 3mm PTFE and switch it out for the 1.75 version. Slide on each heat sink blade and washer.
Align the wooden plates so that the heater block cutouts match up with the wiring.
Hold the plate on top of the wooden aligner and add both screws to reassemble.
Yay, our nozzle can now fit 1.75mm filament! Next We'll move the motor and gears over to the updated extruder mount.