If you have basic soldering skills it's pretty easyÂÂÂ

Look at
www.matey-matey.co.uk for a wiring diagram. If you don't want to cut up the original loom, use some H4 headlight plugs instead of splicing the new loom into the old one, use wire with spade connectors to connect from one plug to another.
Also, looking at the diagram repeat the whole circuit for main beam if you want that uprated as well, including another realy
Alternatively, dizzie on this forum sells them if you get be @rsed.