Can I change headers (eg 'post' to 'respond')

I have just activated forums. It's an easy set up, but I'd like to do some basic configuration to make the language more consistent and logical.

First priority is to change the headers for submission as follows:

Index: change 'NEW' to 'ADD NEW' or 'ADD NEW TOPIC' (depending on what fits).

Topic page: change 'New Post' to 'Respond to topic'.

Can this be done, and if so, where is the code that needs to be changed?

Thanks in advance.