Fatal Error When Logging In

I receive this error when trying to log in as admin:

Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 30720 bytes) in /data/25/2/132/10/2458499/user/2693077/htdocs/merc/wp-admin/includes/post.php on line 1684

I’m not very familiar with this, I’m mostly tasked with updating posts for my employer.

The page I need help with: [log in to see the link]