Mine came from Garrison with no instructions so I did it with the help of this thread;
viewtopic.php?f=65&t=177300&p=1516596&hilit=hykee+custom#p1516596
However I noticed a few things along the way which might help.
Firstly, if you engage the door catch into the locked position with the door open then you can work on getting the lock out without the horn keep sounding. Pull and hold the opening leaver when pushing the catch back to open when you've finished.
It is actually step 1 on the instructions but it seems lots of folk miss it and annoy the neighbours instead (suppose it might be intentional)
When removing the doorcard there's a screw behind the little red reflector - you need to slide the reflector out and you can access it to do so inside the door pocket.
Once I had the doorcard off I found it easier to access the lock area with the window slider removed.
This picture shows the small sprung catch that holds the lock in and the much larger Hykee one. Looking at the small amount of metal on the original its no wonder thieves find it easy to twist the whole lock out.
The Hykee catch is not sprung so needs to be removed prior to fitting the lock and reinstalled afterwards (I think I have it fitted backwards in the pictures so please confirm how its supposed to be when yours turns up).
Here's a picture of the catch in situ, it would not go in the other way around which is why I think you need to check when yours arrives:
Hope this is of some use to someone.
Tap.