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]{Frame title}
...
\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.