Fatal Memory Error from Hummingbird

Hello,
When I try to select Hummingbird in the Dashboard I receive the following message:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 85 bytes) in /home/fresnoai/public_html/wp-includes/meta.php on line 838

My site has also crashed. I am unable to deactivate the plugin and I'm unsure of how to fix the issue.