For such advanced scenarios, I think an option would be an overkill. I expect someone who has such expertise is able to edit
/etc/fstab and change the value e.g. to 32MB in last line:
tmpfs /var/www/moodledata/sessions tmpfs size=32M,mode=775,uid=www-data,gid=www-data 0 0
then reboot or launch
sudo mount -a.