First you need to find the largest directory.
cd /
sudo du -xh --max-depth=1 | sort -h
Ubuntu Find Largest Files and Directories
Ubuntu Find php.ini File
To modify your PHP settings you need to edit the php.ini file.
There are some possible locations on Ubuntu for php.ini like
# locate php.ini
/etc/php/8.3/apache2/php.ini
/etc/php/8.3/cgi/php.ini
/etc/php/8.3/cli/php.ini