There are two ways, both start from the left navigation (the blue column on the left when you have your quote open.)

You can hit Save (the floppy disk), then an orange line appears that says Save As.  If you Save As, you can enter a note, like “Save with “$500 deductible.”  On the Dashboard, you will then see 2 quotes.  You can go in and tweak one for a different version.

Also from the left navigation, there is a “File Actions” button half-way down.  You can select that, then select Create New Quote session.  That will create a copy of your quote as well.