Plugin Tweeter feed

I am using this tweeter feed on my site : http://3doordigital.com/wordpress/plugins/wp-twitter-feed

I want to limit the number of feed we see to only the last 2 tweets instead of 5. On their website they say there is a way to customize but they don’t explain how to do it. They say we can customize with the value num.
default is 5.
num 5 1-15 The number of tweets to display.

But I have no idea where to insert that code and how to insert it.

Anyone knows ?

Thank you.