There's something very weird with this one...

Exporting to JPEG or PNG from a new document takes your default values (i.e. the settings you used the last time you exported) So all the dialogue shows is filename and folder and nowhere a possibility to change the settings

If you choose Export and you chance the filetype to GIF or TIFF you're presented with a second dialogue were you can make alterations to the settings. Once done and choosing Export to JPEG or PNG again the export dialogue suddenly shows the settings button!

So: Xara: please have a look at this issue for I fear we have a bug overhere.