Assuming you have FileMaker Pro Advanced, it is under Tools > Developer Utilities
Check out this link on the FMI site to see what the FM Advanced version includes that FM Pro version doesn't have. There is also a link to info on upgrading on their page:
but really... get yourself FMPA13... Runtimes have come a long way in the 7 or so years since 8.5 and so has FileMaker. Any redevelopment you do in 8.5 can be reduced dramatically in time by using v13...