FrameMaker doesn't have a way to update paths in every file in a book. Assuming all the graphics used in a file are in the same location, opening the file and updating the location for the first graphic will fix all the graphics in that one file.
If you have a lot of files, though, you might want to look into Rick Quatro's PathChanger script, which writes out all the paths in a book to an Excel file, lets you update the Excel file, and then writes the updated path information back into all the files in the book. If you make a "book of books" that includes all the books you are working on, you can get them in one fell swoop.
NB: I haven't used the script. I rather expect that if you have a lot of files that both the write out and the write back will take a while, and of course the editing in Excel is going to be tedious.