If, like most publishers, your publisher expects you to conform to pretty much any style guide regarding the spelling out of numbers, you are going to want to double check that you caught them all. If you want use search to ensure you have caught all the numerals that should be spelled out, you can set up a search using wildcards to pick them out.
Open the Find dialog (Ctrl+F)
If the left sidebar opens up for you (instead of the pop-up), click on the down arrow at the far right of the search box and select Advanced Find
Click on the More>> button
Check Use Wildcards
Then, as your search string, enter [0-9]*
Now you can click Find Next to advance to the first number. Obviously you don’t want to do a straight Replace using this method, but it is an easy way to jump to each numeral so you can make a decision on what to do with it.