After trying several search and replace utilities, I cannot find one that will do a simple search and replace on multiple web page files (.htm)

I'm trying to replace an old java script on all my pages with a new java script.

I want to paste the old script into the find field and paste the NEW script in the replace field.. and be done with it!

Is there a simple utility that will do this? (My web editor will only search and replace one line of text at a time).