To replace text in all the files in a directory, recursively, you can use grep.
sudo grep -rl texttoreplace /somedirectory/ | sudo xargs sed -i ‘s/repacethis/withthis/g’
sudo grep -rl oldtext /example/directory/ | sudo xargs sed -i 's/oldtext/newtext/g'
The g on the end, lets it replace all the instances of the text in each file.