Skicat,
you can download the
user manual for Mares Spark mim / Sten / Cyrano at the official Mares website:
http://mares.com/download.php?region=ITA&id=2387
However, the technical drawings in the
dealer manual linked in by Marwan are much better.
You do not necessarily check the current pressure with a gauge. You can simply depressurize it and reload with the pump strokes indicated in the manual for your model / size of airgun to the desired pressure. That is after you get a new pump

. If you can describe the handle, I will be able to tell you which model you actually have / which manual and pump stroke table applies.
Cheers, ulysses