Can’t login admin after 6 mth away

I can log in to the site but when trying to click the link ‘site admin’ to get to the dashboard i get a blank white page with this error.

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 458288 bytes) in /home2/invest/public_html/blog/wp-content/plugins/simple-forum/sf-includes.php on line 306

Ok so i thought change the simple-forum plugin folder name on the server to simple-forum2 stop the simple press forum from loading but then i get a different error message for something else. This one.

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 1050872 bytes) in /home2/invest/public_html/blog/wp-admin/includes/admin.php on line 40

Not being able to log in to deactivate any plugins how can i get into the main dashboard? What’s this memory size thing?

My site was working fine to log into over 6 months ago but since returning is coming up with this error. My site itself loads fine!