When you download a Label from Zubi the format of the PDF that is created will be set to the default sizing. 

This default sizing may not work for you, e.g. all the text may not fit on the label.

To change the label size; margins to which the data will print; the size of the main font or header font, click the Label Format button on the Reporting tab.

Change the numbers in the boxes and close the screen using the X - it will save the numbers automatically.

Next time you download a label it will use the settings you chose and the PDF will look different. 

Keep adjusting the numbers in the label format screen till you get a sizing that works for you.

As long as you stay in the Reporting area of Zubi, the numbers you have added into the Label Default screen will remain.

To learn about printing labels created by Zubi see here.