IF you are trying to use the Ctrl+F to find and replace well you can’t. at least I dont know how.
but if you have a cell say A1 that contains the following : “stack,overflow”
then if you type this in A2 it should work: =SUBSTITUTE(A1, “,”, char(10))
https://support.google.com/docs/bin/static.py?hl=en&topic=25273&page=table.cs
you can then copy the content of A2 and in A3 right click -> Paste Special… -> Values Only.
Hope this helps
UPDATE 2016-AUG
Google Spreadsheet now support searching for newline using \n here is how:
Edit -> Find and Replace
