Not enough disk space to install - how to Remove extra volume?

My install routine say “not enough disk space to install”
I’ve discovered that there is an extra volume on the boot drive that almost fills the drive.
Two volumes display in Disk Utility (but other utilities show 5 volumes)
One is current install - Catalina
One volume is my old Mojave install. 95GB

Is there a way to remove the old volume without reformatting the entire disk?
I don’t want to loose all my installed applications.

Author: michaelbp