Fine black dust under stepper motors

I bought a secondhand vertex, so I have no idea how much use it has had, but I have been printing quite a few pieces the last two days and I noticed fine black dust falling down under the stepper motors, this combined with printing off the axis every now and then makes me guess the belts are wearing out fast.
However since I did not build this printer I am not sure how to adjust tensioning. I am talking about the small belts, and at first sight I don’t see any way to loosen them.

Is wear on the belts normal? How often do they get changed?

If the pulleys are not correctly aligned they will rub and cause the dust you are talking about.

You can find information on them here.
http://manuals.velleman.eu/article.php?id=16 and here http://manuals.velleman.eu/article.php?id=17

You may want to look at this link as well.
http://www.k8xxx-3dprinters.crimed.be/w/index.php?title=XY-Carriage_Alignment