Double Glazed Door?

On the handle/locking plate, on the inside, a few screws, undo them, the inside plate will be loose, the outside plate can be removed, on the edge, usually 1 long bolt goes into the lock barrel undo that, and you will be able to withdraw barrel, you may need to turn it slightly to a locking postion to remove. Measure the length of the barrel each half, some are different lengths. Fit new one, 10 minute job if that

SD
January 2012