Changing double character space between end of each sentence to single

If I really have to change the spacing to make formatting better for the word processor, how can I do it without having to rewrite my whole book?

Find and replace? Find a period followed by two spaces and replace with a period followed by one space.

Read these guidelines and ask a good question. In particular, what is double character space? Two consecutive space characters or what?

I was trying to get rid of a double character space at the end of every sentence. I was able to change this in tools>options>language settings>English sentence checking. Under punctuation I checked the box for sentence spacing.

Please, edit your answer to elaborate more. I have no such options in my Which is your LO version?