Fatal Error when doing anything

When editing a page or doing anything in wordpress I keep getting a message like:

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 122880 bytes) in /home/marblede/public_html/nkhc.co.uk/wp-admin/menu-header.php on line 98

and

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 30720 bytes) in /home/marblede/public_html/nkhc.co.uk/wp-admin/includes/class-wp-upgrader.php on line 849

each with different file names..

any ideas as to what is going on?

Thanks in advance

Vicky