Stats on equipment are random. The vampire boots can not be upgraded; only the dragon and silver breastplates can be 'upgraded', though the new stats are not necessarily going to be better than the old (you can buy back the original dragon breastplate, if you wish).
If you quick save before running your mouse over an item/chest/merchant or hitting the alt key, you can identify the item or trade with the merchant, then quick load to get different stats or inventory. This can be done repeatedly to get the best stats or specific bonuses on an item (save after finding good candidates) or looking for specific items (such as spellbooks or charms) from merchants. Don't waste too much time with this, though, it really isn't necessary to get the best possible equipment.
