Okay, I'm trying to use my own php.ini file, so I edit the .htaccess file to look like this:

suPHP_ConfigPath /home/u471282391/public_html/

The file is /home/u471282391/public_html/php.ini

But when I update the .htaccess file, everywhere I go on my site returns Internal Error 500.

The contents of the php.ini file are:

post_max_size = 50M
upload_max_filesize = 50M

Do I need to edit the files differently or does php.ini need to be in a different directory?

Remove the trailing slash:

suPHP_ConfigPath /home/u471282391/public_html