Olá, tenho um site WordPress e como é antigo (muito antigo!) como posso esconder os erros de PHP?

Por exemplo, eis alguns dos erros:

• Os submenus não estão a aparecer devido a uma classe Walker.
• Os estilos desapareceram! Em vez de mostrar Areal como tipo de letra, é apresentado Times New Roman.

Eis os erros que estou a receber (a propósito - não consigo aceder ao painel de controlo administrativo por causa deles!)

Warning: Declaration of New_Walker_Category::start_el(&$output, $category, $depth, $args) should be compatible with Walker_Category::start_el(&$output, $category, $depth = 0, $args = Array, $id = 0) in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/theme-functions.php on line 119
Warning: Declaration of DropDown_Nav_Menu::start_lvl(&$output, $depth) should be compatible with Walker_Nav_Menu::start_lvl(&$output, $depth = 0, $args = NULL) in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/plugins/dropdown-menus.php on line 119
Warning: Declaration of DropDown_Nav_Menu::end_lvl(&$output, $depth) should be compatible with Walker_Nav_Menu::end_lvl(&$output, $depth = 0, $args = NULL) in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/plugins/dropdown-menus.php on line 130
Warning: Declaration of DropDown_Nav_Menu::start_el(&$output, $item, $depth, $args) should be compatible with Walker_Nav_Menu::start_el(&$output, $item, $depth = 0, $args = NULL, $id = 0) in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/plugins/dropdown-menus.php on line 144
Warning: Declaration of DropDown_Nav_Menu::end_el(&$output, $item, $depth) should be compatible with Walker_Nav_Menu::end_el(&$output, $item, $depth = 0, $args = NULL) in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/plugins/dropdown-menus.php on line 181
Warning: Declaration of TGM_Bulk_Installer_Skin::before() should be compatible with Bulk_Upgrader_Skin::before($title = '') in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/class-tgm-plugin-activation.php on line 1977
Warning: Declaration of TGM_Bulk_Installer_Skin::after() should be compatible with Bulk_Upgrader_Skin::after($title = '') in /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/class-tgm-plugin-activation.php on line 1999
Warning: Cannot modify header information - headers already sent by (output started at /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/theme-functions.php:0) in /home/vipozico/old.mychinesenow.com/wp-content/plugins/seo-cleaner/includes/class-seo-cleaner.php on line 244
Warning: Cannot modify header information - headers already sent by (output started at /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/theme-functions.php:0) in /home/vipozico/old.mychinesenow.com/wp-includes/pluggable.php on line 1329
Warning: Cannot modify header information - headers already sent by (output started at /home/vipozico/old.mychinesenow.com/wp-content/themes/nollie/functions/theme-functions.php:0) in /home/vipozico/old.mychinesenow.com/wp-includes/pluggable.php on line 1332

Sei que no wp-config.php na raiz do sítio existe uma linha de código:

define('WP_DEBUG', false);

mas como é que o posso editar?

Obrigado!