# replace and write edited version into new file
sed 's/oldstring/newstring/g' file.txt > new_edited_file.txt
# to use with Linux pipe |
cat file.txt | sed 's/oldstring/newstring/g' > new_edited_file.txt
# edit directly in original file: replace original file with new edited version (option -i)
sed -i 's/oldstring/newstring/g' file.txt