To squeeze a little extra material into a Beamer slide, you may specify a shrink-factor for that slide, as in:
\begin{frame}[shrink=5]
...
\end{frame}
This will scale down the contents of the slide by at least 5 percent, and more if needed, so that the contents fit completely within the slide.
For best results, you should specify a shrink factor as close to the needed amount as possible. If your specified value is inadequate, Beamer will issue a warning to let you know. Adjust the shrink factor so that the warning goes away. Otherwise the slide's horizontal spacing will not be optimal.
You should not abuse this feature -- a small amount of shrinkage may go unnoticed, but too much shrinkage can be visually unpleasant.
Instead of shrinking a slide, consider rewriting its contents or perhaps splitting it into two slides.