Keep the post date but removing the circle

1- Activate Jetpack Custom CSS features
2- Add in these code:

.article .post-date {
 background: #fff;
}

.article .post-date a {
 color: #000;
}

Hope that helps.

Thank you! I have one more question:
How can I edit the read more message on posts?
Hope you can help me and thank you again!

This should help you: https://codex.www.ads-software.com/Customizing_the_Read_More

But please note that this is some extensive customization, if possible work on a child theme instead: https://codex.www.ads-software.com/Child_Themes