Before uninstalling your FileMaker software ensure a backup is taken of your Streamtime databases present on and a copy is saved to an external source.
The default location your backups files are stored to on the Server machine are here - Finding Streamtime Databases on your FileMaker Server
Uninstalling Filemaker Server from your server machine
Check which version on FileMaker Server you are running, then follow the instructions to uninstall the software for your version. Streamtime Support can provide you with the original software installer files for you old versions of FileMaker if you need them.
You can also the uninstaller from the following location:
/Library/Application Support/FileMaker/FileMaker Server/[FMVersion}Uninstaller.app
Uninstalling Filemaker Pro from your client machines
Check which version on FileMaker Pro you are running, then follow the instructions to uninstall the software for your version.