Can anyone tell me how i will install the leica diagonial eyepice? I bouht from ebay for some vertical shots, but I think a piece is missing. Maybe a ring? Did anyone use something like this? 
There are, as I recall, 2 different eyepiece mounts on Wild/Leica instruments. If your instrument is branded Leica it has the new-style mount, and I think the right-angle eyepiece you have should work.
In order to install it, you first need to remove the straight eyepiece. Grasp the serrated ring behind the diopter adjustment (the ring that the line behind the 5 in your photo points toward) and twist counterclockwise. That should release the eyepiece and you can pull straight back to remove it. It shouldn't take much effort, so don't force it. Install the right-angle eyepiece by lining up the tabs on its ring with the slots in the telescope and twist clockwise to lock it in place.