If you don't have access the php.ini file you can change 'upload_max_filesize','memory_limit','post_max_size' by doing changes in htaccess file if you have the permission to set these values in htaccess file.
php_value memory_limit 80M php_value post_max_size 50M php_value upload_max_filesize 30M php_value upload_max_filesize 10M
For set these value create a .htaccess file on your website root directory ( if not already exist ) and put the code in this file
If you do not have permission to set these values in htaccess then you will get 500 - Internal server error. For solve this you can contact web server support team.