@GoghGirl - Okay, here's a reg-ex expression that should have you covered assuming the contents of the title fields you're trying to edit look like this:
XX## Title of the Book
Where:
A)The "X's" are capitalized, unspaced letters (representing the series).
B)The "#'s" are unspaced numbers (representing the number in the series).
and
C)There is a space between the last number in the series info and the actual title of the book.
As you can see from the attached screenshot, you
1) select the books whose titles you want to change and do a batch edit (the default keyboard shortcut is E).
2) go to the search/replace tab.
3) select "Regular Expression" as your Search Mode.
4) Select "title" as the Search Field.
5) enter the case-sensitive regular expression as it is shown in the picture (or in the code below):
It should display sample texts and their projected results below (also as per the screenshot attached).
I would recommend you do this on just a handful first (2 or 3) to make sure it works as intended. If it
does work, I would still recommend doing these search/replaces in small-to-medium-sized batches, so that if you make a mistake, you havent totally screwed up your library. As far as I know, once you hit "Apply" or "OK", you don't get any takesie-backsies.
Any of the more experienced members who could confirm or reject the soundness of this advice, please advise!