If you have FileMaker 5 at the moment I would suggest that you read FileMaker Training Series FileMaker Training Series | FileMaker
There is some mayor differences on how database in FileMaker 5 works vs FileMaker 15.
More then one table in each file
1. Export the data from FileMaker Pro 5.
2. Rebuild from scratch.
3. Import the data.
Chances are FMP isn't the only thing that has changed since you built your current db. Some business process and rules almost certainly are different.