Go to [beacon] -> Access -> Elevate to launch a privilege escalation exploit. Choose a listener, select an exploit, and press Launch to run the exploit. This dialog is a front-end for Beacon's elevate command.
You may add privilege escalation exploits to Cobalt Strike through the Elevate Kit. The Elevate Kit is an Aggressor Script that integrates several open source privilege escalation exploits into Cobalt Strike. https://github.com/rsmudge/ElevateKit.