how to change text for shipping costs in checkout

[Pompidompie]

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

[mc12345678]

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.