Change "Post Comment" to something else

I'm setting up an In-Memory page for one of my clients. I'm using the Wordpress blog feature to post individual obituaries. My client wishes to have the option of family/friends to post a "Memory." I've enable comments for the post.

My question: Is there any way to change the text that says, "Post Comment," and the button text that says, "Submit Comment?"

We would like it to say something like, "Add a Memory."