How to remove CLUSTERs and 'partitioning tables'

Hi guys,

   just a quick and probably stupid question. When I make a cluster
based on an index on a table, how can I remove it later? Should I
'create' a new one by using the primary key index?

   Also, can I have more than 1 cluster on my table? Let me explain ...
can I put for instance the record with, let's say, age between 10 and 20
on a specific cluster, from 20 to 30 on another one, and so on?

Thank you
-Gabriele