Simply convert the files with your data and import into your converted/update files.
Open your 5.5 file with FMP 5.5 and export the data in common file format: excel, .mer, .tab, .csv Then import that data into your fmp 10 copies.
I'd recommend the first options as you should be able to use the matching fields option to align your fields quickly and without error. (As long as you haven't renamed any fields in your converted files, of course). That's how I did it with my 5.5 to 10 imports when we made the change.