How to modify the labels "Your name", "E-mail" and "Homepage" inside the comment form?

Hello,

I have one website. It is in English language. I want to change the text of the labels inside the comment form.

I want, for instance, to change "E-mail" to "E-mail (optional)" or "Homepage" to "Homepage (if you have one)". How to do that? What do I need to modify and where ? DB or php file ? Can a custom module do that ?

Alternatively, I can consider adding some single line text under the text area for "Homepage" (similar to the line "E-mail" has: "The content of this field is kept private and will not be shown publicly."). Is this possible, how to do it ?

Any help is greatly appreciated. Thanks.

Attention: I have posted this question at the general post installation forum. However, I received ideas that don't work with Acquia Marina. So allow me kindly to post it again here.