You'll need to swap new copies of your files for the files they are using. Create a script that imports all data from their current copy into the new copy and that also updates the next serial value of every serial number field. You can then run the script, then switch the files.
To minimize the number of times you need to import the data, use the Data Separation model so that the interface elements of your database exist in one file and the data tables exist in the other. This enables you to swap out updated interface files without needing to import any data.
See this thread for more on the data separation model: Convert to Seperation Model