Hi,
Upgrading HikaShop is like making an update.
We always recommend to make a backup but, all of your configuration would kept, like all of your products and your view overrides.
We store overrides in a "extern" directory in order to be sure that Joomla would not delete it while uninstalling or reinstalling the component.
All version of HikaShop uses the same views. During the upgrade, some new files would be added and some files would be upgraded.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.