You can use css to style the
line-height property of your html. Something like this:
That will change the line-height for all content-editors on your page. You might also want to apply that to some other selector as well, perhaps
In general small line height is more difficult to read. And of course it depends upon the font as well.
Calibri has a fairly tall x-height -- the height of lower case letters, like x, compared to capital letters or letters with risers/descenders. The conventional wisdom is that fonts with tall x-height need a little bit more line spacing to help with legibility. So I would recommend not making it too small. (unless, of course, you don't want people to read it!)
Just realized that you might not know how to add css to a page....
Add a script editor webpart to your page. Edit the snippet and place the code from above. That will just change it for that one page.
If you want to change it for your whole site, you might create a css file using a text editor or something like dreamweaver. You can then put that file in your style library or site-assets folder. You can then add that style to your masterpage or page layouts.