Registering our address

We are living in Las Palmas for at least 6 months.  We have Spanish residency cards.

We are under the impression that we must register our address with the local town hall, as we are here for longer than 90 days, and I wondered if anyone could advise on:-

1.  If this is, in fact, the case, and

2.  How we go about doing this

I have done a bit of a Google search, but not found anything conclusive.  It's always easier, of course, to hear from someone who knows the system.

Thanks for any help / adviced

UPDATE:  We have now done this, using the help of a superb translator.  If anyone else needs to cut through difficult to understand Spanish tasks, and wants s Spanish local to help, I'll let you know her details  (35 Euros an hour, which I considered money well spent)

Helen