Limitar tamaño de un archivo al enviar

Deprecated: Function set_magic_quotes_runtime() is deprecated in /home/itworks/public_html/inc/class_core.php on line 165
Limitar tamaño de un archivo al enviar

Han ocurrido los siguientes errores:

Warning [2] Cannot modify header information - headers already sent by (output started at /home/itworks/public_html/inc/class_core.php:165) - Line: 1558 - File: inc/functions.php PHP 5.3.10 (Linux)

File	Line	Function
[PHP]		errorHandler->error
/inc/functions.php	1558	header
/inc/class_session.php	360	my_setcookie
/inc/class_session.php	98	session->load_guest
/global.php	56	session->init
/showthread.php	21	require_once

File	Line	Function
[PHP]		errorHandler->error
/inc/functions.php	1558	header
/inc/class_session.php	365	my_setcookie
/inc/class_session.php	98	session->load_guest
/global.php	56	session->init
/showthread.php	21	require_once

File	Line	Function
[PHP]		errorHandler->error
/inc/functions.php	1558	header
/inc/class_session.php	106	my_setcookie
/global.php	56	session->init
/showthread.php	21	require_once

Warning [2] Cannot modify header information - headers already sent by (output started at /home/itworks/public_html/inc/class_core.php:165) - Line: 352 - File: inc/plugins/google_seo/redirect.php PHP 5.3.10 (Linux)

File	Line	Function
[PHP]		errorHandler->error
/inc/plugins/google_seo/redirect.php	352	header
/inc/plugins/google_seo/redirect.php	340	google_seo_redirect_header
[PHP]		google_seo_redirect_hook
/inc/class_plugins.php	101	call_user_func_array
/global.php	96	pluginSystem->run_hooks
/showthread.php	21	require_once

File	Line	Function
[PHP]		errorHandler->error
/inc/functions.php	1558	header
/inc/functions.php	1619	my_setcookie
/inc/functions_indicators.php	54	my_set_array_cookie
/showthread.php	456	mark_thread_read