Hi,
HikaShop upgrade is like HikaShop update.
You database content would not be affected and your view overrides would be kept.
If you have modified some HikaShop core files (if you have modified HikaShop files directly by ftp) you could loose this data.
All HikaShop overrides (for views, for css), configuration, products, categories (all information stored in the database) would be kept during updates and upgrades.
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.