Right click on the clock/date and click 'Properties'
Near the bottom of the 'Clock Properties' dialog box is Clock Options > Format:
There are some 'preset' options or 'Custom Format'
I use this set
%a %b %e %l:%M %p (copy and paste to try)
Gives me: Sun Sep 10 12:30 PM
Using upper and lower case letters A and B will give you the full spelling or abbreviated wording, Sunday or Sun, September or Sep and so forth
Have a play with this website
http://www.foragoodstrftime.com/It has a 'build your own' where you drag and drop and can see the code (syntax) building as you add them. Again, copy and paste from the website.