how to change text for shipping costs in checkout

I'm working on the checkout staps.
So far i got some changes done to the text for shipping costs.
2 things i can't find, where to change.

I use zone rates for the shipping.
In mijn checkout process I would like to change this line, for orders below € 20,-:
Zone rates (Shipping to NL (1 x 0.00lb(s)))
in to this:
Shipping costs

When above € 20,- it's free shipping.
Then that same line now says:
shipping
I would like that to be:
Shipping costs

Also, shipping details, shipping method.
Shipping to NL (1 x 0.00lb(s))
to
Shipping costs

I can find where to change lbs and zone rates, but not where to remove and changes the whole line

If you have found where to change lbs and zone rates, then you probably have found the CONSTANT that is in the define('CONSTANT', 'value'); function for it.

If you then search for the CONSTANT using tools->developers toolkit you should find a function that uses that constant. Then perhaps that function is used elsewhere and the process continues until you find where it is used.