You have to change the settings in your php.ini file to allow larger uploads. There are a few settings that might need to be updated. A quick google search on the issue came back with: https://stackoverflow.com/questions/2184513/change-the-maximum-upload-file-size
You can set a custom 500 error page using your htaccess page. Another google search came back with: https://stackoverflow.com/questions/25869504/htaccess-show-404-403-500-error-pages-via-php