How does fread know when the file is over in C?

So I'm not entirely sure how to use fread. I have a binary file in little-endian that I need to convert to big-endian, and I don't know how to read the file. Here is what I have so far:

FILE *in_file=fopen(filename, "rb");
char buffer[4];
while(in_file!=EOF){
    fread(buffer, 4, 1, in_file);
    //convert to big-endian.
    //write to output file.
}

I haven't written anything else yet, but I'm just not sure how to get fread to 'progress', so to speak. Any help would be appreciated.