Disk quota reached and Cannot delete Log file


I have written a few pages of PHP. I have no images and a small database and yet my storage is full.

I ran:

$ du -h -t 50M /

which returned:

3.6G /nix/store
2.0G /home/ubuntu/lib/apache2/log
2.0G /home/ubuntu/lib/apache2
2.0G /home/ubuntu/lib

I ran

cd /home/ubuntu/lib/apache2/
rm -rf /log/*

but when I checked the log file was still 2.0GB

How do I delete the contents of the log file and can I remove the nix store file?