you will probably want to alter a few configuration directives. either in php.ini or in your program
post_max_size //only can be set from php.ini or htaccess
upload_max_filesize //only can be set from php.ini or htaccess
max_execution_time //can be set from script.
on top of changing those you need to hope your browser itself wont think nothing is happening and timeout after a few minutes. otherwise those three should help.