upgrading versus fresh install

[Matt H.]

Hi
I usually do a fresh install of each new release. If however I wanted to
do an upgrade instead (I want to re-install), what aspects of my
current configuration/installation would be saved and what would be
changed?

For example, all the up2date updates I've installed would be kept? That
would be my main worry. How would all my custom config files be dealt
with? Browser plugins, bookmarks, personal $HOME files etc?

Thanks
-- 
Matt