Look in the lower right of the plot dialog, see an arrow in a circular button, press that. Part of the plot dialog is tucked away because you are "supposed" to be using Page Setups-- which are actually pretty good, save time, remove need to remember to check boxes like "portrait" == give them a shot!
A good way to solve that is: Go with a right click on label model on your bottom left and choose page setup manager, and modify *model*, in there you can set the printer, print window and landscape or portrait for all layouts and your model space, doing that you will set all drawing even if close the draw and open again... saving your time! or you gonna set every time you wanna plot.