Change font from bold to regular

Hi!
I am using “Origin” theme, but I have a problem.
The theme was working well until I changed the logo… Then the font became bold only in Greek letters.
So it is like that now:
Sidebar Menu: https://i1197.photobucket.com/albums/aa431/AniTuts/Capture-3_zpsbaa70dba.png
Post: https://i1197.photobucket.com/albums/aa431/AniTuts/Capture2-1_zps15d371d1.png
I ‘ve already tried reinstalling the theme but it still appears like that…
It is really disturbing so I would like to know if there is any way to fix it.
Thanks in advance!