Change the language of the date & time?

Hello,

I’m using a theme called “German Newspaper” that has a time\date at the right hand corner. The blog will be in Spanish and I have translated the entire blog into Spanish. However, I failed to understand how to change the names of the days \ names of the months from English to Spanish. I suspect that this has something to do with WordPress and not with the theme itself. I do not wish to install an all-Spanish WordPress version, I just want to change the time and date…

Any easy way to do this…?

Thank you.
Yoav.