First up you need to remove the speedo housing from the car, see how here.
Remove the cover (silver in picture) by pulling away from the speedo face.
This will uncover several clips running over the top,
unclip these starting from one side and work your way over.
Once the back is off it will uncover several clips running all the way around.
They are black clips over white except for one.
With those unclipped the back will come free, carefully remove the old face trying not
to touch the needle. With the old face off clean up and old glue and place the new face
in position, again, not touching the needle.
There is no need to use sticky pads or glue on these dial
faces as it is held in place when the speedo is rebuilt.
Before you reassemble, make sure there are no finger prints or marks on
the face, this can be annoying when you put it back together.