The most up-to-date version of FileMaker Pro 8.0 is 8.0v3, so you have the latest update.
Version 8.5 was a paid upgrade from 8.0, so you would not be able to obtain it. The most current version of FileMaker Pro is 9.0v3.
sorry but to upgrade from 8 to 8.5 you had to pay !
So now you can upgrade directly from 8 to 9 ( paying ) or wait to the next version ( FMX ? )