I am having a problem with the text on the submit K2 comments. It is showing as "K2_SUBMIT_YOUR_COMMENT"
How do I change the button name ?

Hello,

Are you using any language overrides or a custom language pack?
You can also solve the issue by adding a temporary language override (google to see how to) for the "K2_SUBMIT_YOUR_COMMENT" string.

Thanks for the quick response.
I am using the standard GB(en).

I tried to do an override but the Language Constant is called "K2_SUBMIT_COMMENT" I created a new override with that but it does not change the text on button.

The comment button shows "K2_SUBMIT_YOUR_COMMENT" vs "K2_SUBMIT_COMMENT"

Is that the reason why the comment button text is not affected?

Yes, the template might have a wrong language string.
Did you create an override for both strings?