When you go to export the file and the "EXPORT" box pops up where you select your file type make sure that "Supress Options" at the bottom is not checked and then hit the "Save" button. That lets you into the tabs so you can set your compression and resolution.
We used FlexiSign for 10 years before we figured that out.
Keep in mind that a 300 DPI file saved in Flexi is a bigger file, but seems to have less resolution, than a 300 DPI in Adobe or Corel. PDF is your friend...and not an option in Flexi.