I translating theme in Finnish. How do i change the language?

I´m using poedit to translate this theme in Finnish Language. I found language files and now have 65% translated them, so i decided to try it out whether it works or not. I saved files in fi.po and fi.mo to language file. then i packed the file and uploaded and intalled it. It seems you have to do something else also as it still appears in English aswell