Hi Paulo,
To "hold" is to support something or grasp something using your hands.
Example: They were told to hold the portrait for the auction.
To "uphold" means to make sure a certain virtue (good principle), custom or practice is being observed and carried out.
Example: Hard work, integrity and honesty are values we must uphold in this school.
As a side topic, another two sets of words I can think of are: "set" and "upset" / "root" and "uproot". They have different meanings.
Hope this helps.
Cheers, Lance