Please help me to translate default WordPress theme strings…

Hi, I am translating a wordpress website but how can I translate the defaults fields that belong to the theme not set by the webmaster? I don't find any edit box for these!
For example there is a "Search box", and I don't find any field for it?
And also there is an "Upload box section" and "Select the file to upload", these strings are automatically written by the theme, how can I change the WordPress theme language to change all these strings at once?