Zorin 17 Pro upgrade problems - can I do a clean install

Hi, Ive upgraded from 16.3 Pro to 17pro & having some issues that Helpdesk cant resolve. Mainly Sushi wont work in Nautilus . (It worked in 16.3 ) I installed lots of stuff to try & find an alternative & have ended up with junk everwhere which I can't uninstall .

I want to do a clean install, how do I save my application settings & passwords & how do I load then into a fresh install. Will backups do that without copying over all the leftover junk I dont need ??

And can I use the code I got when I purchased the upgrade in a fresh install of 17 pro.

thanks .. Don.