How do I set my settings to display the siz...

You don't tell us what email program you are using.
Assuming you have Windows Vista and are using Windows Mail, just open your inbox, right click any column title on the email display window, select "Columns..." and then scroll down the list of available information items and check "Size", so that a column showing the size of the emails shows. You can then place the column in the position you want (just left click the colum title and hold and then drag and drop the column in the new location).
I have not presently installed Outlook in my computer, but I think the proceedings were just about the same.