TOPIC: Customise registration form

Hi,
I am trying to customise the Joomla registration form at this URL victoriandefencealliances.org.au/index.php/create-web-account
I want to customise the text I have circled in red in the attached screen grab.
I managed to find a language override for the Interest Groups but I can't work out how to change the other text / labels.

- I need to remove the title that says "Newsletter"
- Change the text next to the opt-in check box and also remove text "(optional)"
- Remove word text "(optional)" next to the interest groups heading

Great plugin just hoping to customise these things. Appreciate any help.