Trimming nails?

[Ubu Noir]

Hi, just a quick question.  My two gerbils have yucky noses again,
though they're on Carefresh, and with no other wood or plastic products
to cause the balding / swelling.  Holding them, their nails seem to be
really long.  I'm wondering if their normal nose scratching is
detrimental because of their long nails.  How would I go about trimming
their nails?

Thanks,
Kelly