depends on what exactly you want to accomplish.
the easiest though would be to simply add some css declarations
i.e something like
#wppizza-article-prices-xxx {display:none}
or even (better probably, but depends on exactly how your prices are set up)
#wppizza-article-sizes-xxx {display:none}

where the ‘xxx’ equals the id of the menu item.
(might also want to have a look at https://docs.wp-pizza.com/developers/?section=frontend-css-styles-layout )

if you truly want to not display them at all (i.e not even in the sourcecode of the page) you’ll have to get your hand s dirty with some wordpress/php coding/filtering
(if you need that and are happy to do some php coding, let me know and i’ll find some filter that allows you to do that)