Type in the following command
find /var/www/ -mtime -14
this will find all files that where modified within the last 14 days within the /var/www/ directory. We use the -mtime test to get all the modified files.
To only find .txt files that were modified within the last 14 days within the /var/www/directory we would use this command
find /var/www/ -mtime -14 | grep '\.txt'