Editing posts layout

Dear All,

I would like to inquire about the possibilities of changing the texts on the blog of my webpage. The link is here:

http://badzgreen-effective.pl/certyfikat-green-effective-dla-firmy-zaklady-uslugowe-ezt/

I would like to:
1. Change the date format
2. Translate all the texts below the post – “About the author”, “Leave a reply”, “Logged in as”, “Leave your message”, “Send message” (button)

Please let me know how I can do that?

Kind regards
Maria