First, you use FileMaker 11 to convert to .fp7 format, then you use Filemaker 13 to convert to .fmp12 format.
Here's a download link for a 30 day free trial copy of Filemaker 11 you can use for the first step of the conversion:
I also recommend that you read these two Knowledge Base articles on converting your files:
Converting to .fp7 format: http://help.filemaker.com/app/answers/detail/a_id/750/kw/converting
Converting to .fmp12 format: http://help.filemaker.com/app/answers/detail/a_id/10571/kw/converting
Be prepared to invest some time into testing and updating the converted files as there is a good chance that your converted files may not function perfectly. The KB articles cover many, but not all of the possible issues. Feel free to post back here with any issues you encounter that don't seem to have been covered by the KB articles.
Everytime I try the link to the download of v11 it takes me to the main site page...