This will search all text files in the current directory for the word "SOME_NAME" and replace it with my name "Kris". This regex ends with "/gi" which the "i" means ignore case, so it will change any spelling of the word "SOME_WORD" have it be upper or lower case spelling of it.
Note also that you can just type in the full file name instead of "*.txt" and do the one single file.

This is the same as above only difference is it will change it only in files with the name of "filename"