To convert your DIYElectronics Prusa i3 from 3mm to 1.75mm you will need the following two products:
Our standard 1.75mm extruder body and accessories kit - https://www.diyelectronics.co.za/store/diyelectronics/335-charlstruder-for-prusa-i3-kit.html
E3D V6 1.75mm Hotend Assembly - https://www.diyelectronics.co.za/store/hotend-assemblies/1433-all-metal-hotend-for-175mm-filament.html