Check the file permissions to make sure you have write permissions on the files and/or directories.
You are now ready to write your files. Otherwise you must be superuser to do what you want to do.

Since you are using ubuntu (which is debian), it is good to remember to precede any action that requires root privileges by sudo
To delete the file, simply invoke
sudo rm <path_to_file_to_rm>
You can as well change the server persmission to be writable by you by doing
sudo chown -R <your_name> <path_to_lamp_server_folder>
In a real server, changing server permission to a regular user other than root is not advisable!

Happy Times!